what is sensory and motor system. Types of senses , their receptors and pathways. Motor system organs,their disorders

1. Neurobiology of sensory-motor systems and internal environment :
Organization of sensory- motor systems in terms of receptors
and thalamocortical pathways and motor responses
BIOLOGICALFOUNDATIONSOF BEHAVIOUR-UNIT4
Presented by :
Sakshi Maheshwari
M.Phil C.P. 2nd year

3. What is a SENSORY SYSTEM.?
 The sensory system is a complex neural network of pathways that
relay information about the external environment between the brain
and body.
 Sensory receptors pick up data about external stimuli and transmit that
information as electrical signals to the spine and brain. In the brain, the
signals are interpreted, translated, and ultimately perceived as senses.
 sensory system consists of sensory neurons (including the sensory
receptor cells), neural pathways, and parts of the brain involved in
sensory perception and [interoception]].
 Sense organs are transducers that convert data from the outer
physical world to the realm of the mind where people interpret the
information, creating their perception of the world around them

4. SENSORY RECEPTORS(classification : type of
stimulus)
Chemical
• chemoreceptors
Pressure
• mechanoreceptors
temperature
• thermoreceptors
light
• photoreceptors

5. SENSORY RECEPTORS(classification : based on
location)
cutaneous
• Found in dermis and epidermis
Muscle spindles
• Are mechanoreceptors that detect stretch in muscles
• Detects distant stimuls eg : vision,hearing
telereceptors
• Detects stimulus outside on the body surface
exteroceptors
• Detects stimulus inside the body
interoceptors

6. SENSORY RECEPTORS(classification : based on
morphology)
Free nerve endings
• Nociceptors and
thermoreceptors
encapsulated
• Remaining cutaneous receptors.
Present for specialised functions

7. SENSORY RECEPTORS AND PATHWAYS
Vision Audition
Tactile Olfactory
Gustatory

8. Vision(PHOTORECEPTORS)
Rods
• Sensitive to dim light
• Used mainly for night vision
• Absent from foveal region
• In dim light acuity is best when looking slightly away
Cones
• Sensitive to bright light
• Used for daytime vision
• Densely packed in foveal region
• In bright light acuity is best when looking directly at things
• red • green • blue

9. Vision(PHOTORECEPTORS)
Bipolar cells
•Photoreceptors
synapse here in
which they
induce graded
potentials
Retinal Ganglion
cells(RGC)
•Bipolar cells
induce action
potentials on
them
•RGC axons
collect in bundle
at optic
disc(blind spot)
and leave the
eye to form optic
nerve
Horizontal and
Amacrine cells
•Contribute to
retina’s
processing of
visual
information

10. Vision(Pathways)
 GENI-CULO-STRIATE PATHWAY
 Major visual pathway
 Runs from retina lateral geniculate nucleus of thalamus primary
visual cortex(V1 ,Brodmann’s area 17)
 Name derives from knee shaped appearance of LGB and striped
appearance of V1.
 Takes part in pattern,color,motion recognition and includes
conscious visual functions
 Symptoms of damage include impairments in pattern, color, motion
perception + Visual form Agnosis (“not knowing”) : inability to
recognise objects

11. Vision(Pathways)
 GENI-CULO-STRIATE PATHWAY
 LGN has 6 well defined layers :
* 2,3,5 : receive fibres from ipsilateral eye
* 1,4,6 : receive fibres from contralateral eye
 The topography of visual field is reproduced in each LGN layer :
central part represent central visual field , and peripheral parts
represent peripheral field.
 This visual field is represented in primary visual cortex – but upside
down, inverted and reversed( the central part is represented at back
and periphery towards the front)
 Vision for light and color are separated throughout the pathway
 Optic radiations : GNP – pathway by which electrical signals go from
thalamus to visual cortex

12. Vision(pathways)
 TECTO-PULVINAR PATHWAY
 Relays from eye superior collicus in midbrain tectum visual
areas in temporal and parietal lobes “ through relays in lateral
posterior-pulvinar complex of thalamus”
 Takes part in detecting and orienting to visual stimulation
 This entire pathway + additional projection from colliculus to cortex
via thalamic nucleus provide information about spatial location of
objects
 Damage can cause : Visual Agnosia(not knowing what)
Visual Ataxia( not knowing where)

13. Hearing (Auditory Receptors)
 Changes in air pressure causes sound waves.
 3 components determine what we hear :
 Receptor cells in inner ear detect these differences in air pressure and convey them to brain as action
potentials
 Areas of cortex in temporal lobe interpret the action potentials as random noise or as sounds
• Speed of
pressure
changes as
changes in
pitch
frequency
• Pressure
changes as
loudness
amplitude
• Perceived
uniqueness or
tonal quality of
sound
timbre

14. Hearing(Pathways)
Axons of hair cells leave the cochlea to
form major part of auditory nerve
This nerve first projects to level of medulla
, synapsing either in dorsal or ventral
cochlear nuclei or in superior olivary
nucleus
Axons of neurons in these areas form
lateral lemniscus , which terminates in
discrete zones of inferior colliculus in
midbrain

15. Hearing(pathways)
Inferior
colliculus helps
in orienting to
sound location
Superior
colliculus
functions to
orient head
towards sounds’s
direction
Conjoint
recognition
occurs i.e.
direction and
visual source of
sound both are
recognised

16. Hearing(Pathways)
2 distinct pathways emerge from colliculus , coursing
to ventral and dorsal medial geniculate nuclei in
thalamus
Ventral region : projects to core auditory cortex(A1/
Brodmann’s area 41). It identifies sound
Dorsal region : projects to secondary auditory
regions. It indicates its spatial source
Projections of auditory system provide both
ipsilateral and contralateral inputs to cortex , so
there is bilateral representation of each cochlear
nucleus in both hemispheres

18. Body senses(SOMATOSENSORY RECEPTORS)
Extroceptive : enables to feel the world around us
Interoceptive : monitoring internal bodily events and informing the brain about the positions of
body segments relative to one another and about body in space
receptors
Pain touch Body awareness
Balance(interoceptive)

19. Somatosensory receptor
Pain(NOCICEPTION)
 It is the perception of pain , temperature and itch
 Most nociceptors consist of free nerve endings
 When damaged or irritated these endings secrete chemicals,usually peptides, that
stimulate the nerve producing action potentials that then convey messages about
pain, temperature or itch to CNS
 It is CNS especially CORTEX that pain is perceived
 Pain receptors are necessary because people who are born without it are subject to
body deformities through failure to adjust posture and acute injuries through failure
to avoid harmful situations
 8 different kinds of pain receptors exist

20. Somatosensory receptor
Pain(NOCICEPTION)
 Some chemicals irritate surrounding tissue ,stimulating release of other chemicals to
increase blood flow . These reactions contribute to pain, redness and swelling at site
of injury
 Many internal organs have pain receptors ,but ganglion neurons carrying
information from these receptors lack pathways to brain
 So ,they synapse with spinal cord neurons that receive nociceptive information from
body surface
 Thus spinal cord neurons carry 2 sets of signals : a)body surface b) internal organs
 But they cannot differentiate between the 2 sets of pain , as a result pain in body
organs is often felt as “referred pain” coming from body surface.

21. Somatosensory receptor
Touch(HAPSIS)
 Hapsis is tactile perception of objects
 Receptors here enable fine touch, pressure allowing us to identify objects
we touch and grasp
 They occupy both superficial and deep skin layers and are attached to
body hairs as well
 When touch is lost ,not only do we lose information that it normally
provides, movement is affected as well ( to the point that it can result in
motor disability , hands feet becomes useless to use in everyday life)

22. Somatosensory receptor
Body location and movement(PROPRIOCEPTION)
They are encapsulated nerve endings sensitive to
stretch of muscles and tendons and to joint
movements
We are ordinarily unaware of how proprioception
contributes to our movements but witness what
happens when this sense is lost

23. Somatosensory PATHWAYS
Body location and movement(PROPRIOCEPTION)
 POSTERIOR SPINOTHALAMIC TRACT
 Make up the hapsis and proprioception system
 Neurons are relatively large,heavily myelinated, rapidly adapting
 Cell bodies located in posterior root ganglia , dendrites project to sensory
receptors in body, axons project into spinal cord
 Dendrite and axon of each somatosensory neuron are joined into one
continuous fibre
 Cell bodies in these nuclei send their axons across spinal cord to form
medial lemniscus , which ascends to synapse in ventrolateral thalamus
 This thalamic nuclei then projects into “primary somatosensory cortex” (S1
or Brodmann’s area 3-1-2) as well as to are 4, the primary motor cortex

24. Somatosensory PATHWAYS
Body location and movement(PROPRIOCEPTION)
 ANTERIOR SPINOTHALAMIC TRACT
 Nociceptive fibres here are smaller ,less myelinated , slowly adapting
 Follow same course to enter spinal cord but once there, project to relay
neurons in more central region of spinal cord, ‘substantia gelatinosa’
 The 2nd –relay cells send their axons across to other side of cord, where they
form AST.
 These fibres eventually join posterior hapsis and proprioception fibres in medial
lemniscus
 They too terminate in ventrolateral thalamus as well as posterior thalamus ,and
these messages too are relayed in turn to areas 3-1-2 of cortex

25. Somatosensory PATHWAYS
Body location and movement(PROPRIOCEPTION)
 ANTERIOR SPINOTHALAMIC TRACT
 A unilateral spinal cord injury that cuts the somatosensory
pathway in that half of spinal cord results in bilateral
symptoms k/as “Brown-Sequard syndrome”
 Loss of hapsis and proprioception : occurs unilaterally on side
of body where damage occurred
 Loss of nociception : damage occurs on opposite side of
injury

26. Somatosensory PATHWAYS
MOTION AND BALANCE
 VESTIBULAR SYSTEM
 Our inner ear contains organs that allow you to
perceive your own motion and to stand upright without
losing your balance
 Vestibular organs contain hair cells that bend when
body moves forward or when head changes position
relative to body

27. Somatosensory PATHWAYS
MOTION AND BALANCE
 VESTIBULAR SYSTEM
 The 3 semicircular canals are oriented in 3 planes that correspond to 3 dimensions(3 D) in which we move ,so collectively they represent any
head movement
 The otolith organs detect the head’s linear acceleration and respond to changes in head position with respect to gravity
 Fibres from balance receptors project over 8th cranial nerve to a no of nuclei in brainstem.
 These nuclei interact in hindbrain to help keep us balanced while we move; they also aid in controlling eye movements at midbrain level
 Finally, through its connection in cerebellum information from vestibular system allows us not only to balance but also to record and replay ,
actively and in mind’s eye ,the movements we have made

28. Somatosensory PATHWAYS
MOTION AND BALANCE
 VESTIBULAR SYSTEM
 “Vertigo” – a sensation of dizziness when one is not
moving , is a dysfunction of inner ear and can be
accompanied by nausea and difficulty maintain
balance while walking
 “Meniere’s disease” – disorder of middle ear
resulting in vertigo and loss of balance , occurs more
in women , and in middle age.

29. Taste(GUSTATORY RECEPTORS)
 The stimuli for taste is chemical
 For taste, receptors are taste buds , which are k/as papillae and help the tongue grasp food , taste buds lie buried
under them
 Chemicals in food dissolve in saliva that coats the tongue and disperse through saliva to reach taste receptors
 Taste receptors are also found in gut and elsewhere in the body where they may play a role in food absorption,
metabolism,appetite
 5 types : sweet, sour, salty, bitter, umami(savory)
1. Sweet – sensitive to calorie rich food
2. Bitter – sensitive to some vegetables and variety of toxic substances
3. Salt- chemicals necessary for water balance
4. Sour- sensitive to acidity esp in fruits
5. Umami- sensitive to protein and esp. to food additive monosodium glutamate

30. Taste PATHWAYS
 GUSTATORY PATHWAY
 3 cranial nerves carry info from tongue :
 All 3 enter solitary tract , the main gustatory pathway
 The pathway divides in 2 routes :
glossopharyngeal
CN 9
vagus
CN 10
facial
CN 7
PATHWAY
Ventroposterior
medial nucleus of
thalamus
S1(sensitive to tactile
stimulation ,
responsible for
localizing tastes on
tongue )
S2 (entirely for taste)
Pontine taste
area
Projects to lateral
hypothalamus and
amygdala (role in
feeding )

31. Smell (OLFACTORY RECEPTORS)
 The receptor surface for olfaction is olfactory epithelium located in nasal cavity
 Composed of 3 cell types : receptor hair cells, supporting cells and underlying layer of basal cells
Axons projecting from
olfactory receptors
relay to glomeruli in
olfactory bulb
From glomeruli ,mitral
cells form olfactory
tract(cranial nerve 1)
Mitral cell projections
reach pyriform cortex
Reach
hypothalamus,amygdal
a, enterorhinal cortex
of temporal lobe and
orbitofrontal cortex

32. Smell (OLFACTORY RECEPTORS)
The outer epithelial surface is covered by layer of
mucus in which cilia are embedded
Odors must pass through mucus to reach
receptors which means that changes in its
properties may influence how easily we can
detect an odor

33. Smell PATHWAYS
 OLFACTORY PATHWAY
 The axons of olfactory receptor relays synapse in olfactory bulb ,which
is multi-layered
 The major output of bulb is lateral olfactory tract which passes
ipsilaterally to pyriform cortex, amygdala, entorhinal cortex
 Pyriform cortex’s primary projection goes to central part of dorsomedial
nucleus in thalamus
 The dorsomedial nucleus in turn projects to orbitofrontal cortex ,which
is primary olfactory neocortex
 Single cell recordings from olfactory pathways suggest 2 general class
of neurons : responsive to specific odors , others general odors

34. What is MOTOR SYSTEM?
 Reserved for those parts of nervous system that take part most directly in
producing movement and for spinal cord neural circuits that issue commands to
muscles throughout peripheral nerves
 The information that directs motor processing comes into the system in the form
of highly integrated sensory information from the sensory association areas,
such as the parietal lobes, and the subcortical structures of the basal ganglia and
the cerebellum. In addition, internally generated motivation for action also directs
movement. The system then directs this information to areas of secondary motor
planning and programming before sending it to the primary motor cortex.

35. STRUCTURES INVOLVED IN MOTOR
PROCESSING
structures
cortical
1.1.Primary motor
cortex(M1)
2.2.Prefrontal
Cortex(PFC)
3. Premotor(PMA)
& supplementary
motor areas(SMA)
subcortical
1.Basal ganglia
2.Cerebellum
3.Spinal cord

36. MOTOR NERVE TRACTS
Voluntary muscle movement
It has 2 types of motor neurons:
a. Upper : this has its cell body(betz’s cell)
in precentral sulcus area of cerebrum. It
pass through internal capsule,pons and
medulla.They make up the pyramidal
tracts and decussate in medulla
b. Lower : this has its cell body in anterior
horn of grey matter in spinal cord. The
motor end plates of each nerve and
muscle fibres they supply form a motor
unit
Involuntary muscle movement
 There are 3 types of reflexes:
a. Spinal : consist of sensory neuron,connector neuron
in spinal cord and lower motor neurons.Its
involuntary and nearly instantaneous movement in
response to a stimulus
b. Stretch (myotatic reflex) : it’s a muscle contraction
in response to stretching within the muscle. It’s
monosynaptic reflex. Provides automatic regulation
of skeletal muscle length.
c. Autonomic Reflex : It involve internal organs.
Urination ,defecation are spinal reflexes that can take
place without input from brain.They are polysynaptic.

37. MOTOR PATHWAYS
Pyramidal(there are large bumps on brainstem’s ventral
surface which look like pyramids)
 Corticobulbar : neocortex sends projection to
brainstem. movement in muscles of head, facial
expressions
 Cortico-spinal :neocortex sends projection to spinal
cord. involved in movement of muscles of
limb,digits,body. Parts that descend from
somatosensory cortex terminate in ascending
sensory tracts which modulate sensory signals that
are send to neocortex
Extrapyramidal
 Rubrospinal
 Pontine reticulospinal
 Medullary reticulospinal
 Lateral vestibulospinal
 Tectospinal
 Causes involuntary actions. Involved in reflexes, locomotor
complex movements and postural control
 Stimulation results in contraction of skeletal muscles &
smooth muscles

38. AREAS WHICH INITIATE MOVEMENT
 POSTERIOR CORTEX : lies posterior to central fissure. Specifies movements goals , sends sensory information
from vision, touch, hearing into frontal regions . More direct routes which execute automatic movements are
directed by primary motor cortex. Indirect routes which execute voluntary movements are directed through
temporal and frontal cortex
 PREFRONTAL CORTEX :on instructions from prefrontal cortex , generated plan for movements that it passes
along to premotor cortex (specialised movements)
 PREMOTOR CORTEX : houses a movement repertoire. It recognizes others’ movements and selects similar or
different actions(simple movements)
 PRIMARY MOTOR CORTEX : consist of more elementary movements including hand mouth movements(simple
movements)

39. MOTOR PROCESSING(cortical
areas)
 The role of the primary motor cortex is to manage the fine details required
to perform movement. The primary motor cortex lies in the precentral gyrus,
or motor strip of the frontal lobes, just anterior to the central sulcus and the
somatosensory strip.
 Neuronal input emanates from the secondary motor areas and from the
somatosensory cortex.
 Neuronal output travels through the internal capsule, and on to descending
tracts of the spinal cord, and ultimately to the muscles of the body.
Damage or disease of the motor cortex results in hemiplegia, or the loss of
voluntary movement, to the opposite side of the body. Hemiplegia is often a
hallmark of stroke to the middle cerebral artery.
 The primary motor cortex and the somatosensory cortex are in reciprocal
communication with each other through a reflex circuit. The primary motor
cortex receives feedback from the somatosensory cortex about the effect of
movement just initiated

40. MOTOR PROCESSING(cortical
areas)
 The supplementary motor area (SMA, also supplementary
motor cortex, or medial premotor cortex) functions in
organization and sequential timing of movement. The internal
intention to move is also a function of this area
 The SMA receives input from the parietal lobes (posterior parietal
association area), the somatosensory strip, the secondary
somatosensory areas, and subcortically from the basal ganglia
and the cerebellum. It also interconnects with the PMA.
 The SMA outputs to the primary motor cortex in both the
ipsilateral and contralateral hemisphere. It also outputs back to
the basal ganglia and the cerebellum (Bradshaw & Mattingly,
1995).
 It functions specifically as a planner of motor sequences.
Electrical microstimulation of the SMA elicits the urge to make a
movement, or the feeling of anticipation of a movement.

41. MOTOR PROCESSING(cortical
areas)
 The Pre Motor Area also plays a role in motor planning and sequencing and
movement readiness. Also contain “mirror neurons”
 The PMA receives neuronal input from some of the same general areas as
does the SMA, but from slightly different places. For example, the PMA
receives parietal input from posterior parietal areas, rather than parietal
association cortex. The PMA receives input from the secondary
somatosensory areas, rather than from both the primary and secondary
somatosensory areas, and receives more cerebellar input.
 It is also reciprocally interconnected with the SMA and projects to the
primary motor cortex and the reticular formation.
 In a general way, the PMA performs similar premotor planning functions as
the SMA, such as the sequencing, timing, and proper initiation of voluntary
movement, but it may function more in externally cued readiness for action,
whereas the SMA provides more of an internal readiness cue.
 For example, when runners line up for a race and hear the official say, “On
your mark . . . Get set . . . Go,” their PMA is most active between “Get set”
and “Go.”

42. MOTOR
PROCESSING(subcortical areas-
Brainstem)
 26 pathways originate in brainstem and
carry messages to spinal cord
 Information related to posture and
balance
 Control autonomic nervous system
 Responsible for whole body movements
 Emotional behaviour also modulated
 Involved in mechanism of
eating,drinking,sex

43. MOTOR
PROCESSING(subcortical areas-
Basal Ganglia)
 It connects motor cortex with midbrain and
sensory regions to neocortex with motor cortex
 A prominent structure here is : caudate putamen
 BG receives input from 2 main sources:
1. All areas of neocortex and limbic cortex,
including motor cortex, project to basal ganglia
2. The nigrostriatal dopamine pathway extends
into basal ganglia from substantia nigra
 There are 2 types of neural pathways : excitatory
and inhibitory .
 Both these pathways converge on globus
pallidus(GPi). It projects to thalamus and
thalamus projects to motor cortex. GPi
determines whether movement will be weak or
strong

44. Disorders of basal ganglia
Hyperkinetic symptoms
 Cells of caudate putamen are
damaged, unwanted, choreiform
movements called ‘dyskinesias’ occur.
EG :
 Huntington’s : involuntary and
exaggerated movements
 Tourette’s : unwanted tics and
vocalizations
Hypokinetic symptoms
 Cells of basal ganglia are intact but its
input are damaged, injury results in
difficulty making movements. EG:
 Parkinson’s : muscular rigidity,
difficulty initiating and performing
movements.

45. MOTOR
PROCESSING(subcortical areas-
cerebellum)
 Participates in maintaining motor skills , has
role in movement timing, helps maintain
movement accuracy
 It has 2 hemispheres and a small lobe k/as
flocculus projects from its ventral surface.
 It is divided into several regions each specializing
in different aspect of motor control
 Flocculus : controlling balance
 Many projections go to spinal cord and motor
nuclei and control eye movements.
 Medial regions : face and body’s midline
 Lateral regions : movement of limbs, hands,
feet, digits

46. DISORDERS OF COMPLEX MOTOR
PROCESSING
When to act
 Akinesia is a difficulty in initiating and maintaining
behavior. Patients with akinesia may be extremely
slow to start or perform a movement, may become
rapidly fatigued when performing repetitive
movements, or may have problems in performing
simultaneous or sequential movements.
 Motor perseveration a person continues in the
same behavior, or constantly selects it in the
presence of other choices
 defective response inhibition a person behaves
inappropriately, displaying a motor response when it
is unwanted
How to act
 Apraxia refers to an inability to perform voluntary actions despite an
adequate degree of motor strength and control. 4 types are present :
 limb-kinetic apraxia (also ideokinetic) people appear clumsy and have
poor motor control. In attempting to show how a key would be used,
limb-kinetic apraxics may make large grasping motions, rather than fine
thumb-to-forefinger movements.
 Ideomotor apraxia involves difficulties in the execution of the idea of a
movement, even though the knowledge of the action is preserved.
 With conceptual apraxia, in contrast, the knowledge of the action has
been lost. For example, when asked to gesture how to use the key, the
person may perform any number of vague movements
 Dissociation apraxia (formerly ideational apraxia) involves impairment
in an action sequence. This type of apraxia can be witnessed in a
multistage request such as, “Show me how you would pour and serve
tea.” Actions may be performed out of order, although the individual
actions themselves are correct

48. REFERENCES :
 https://study.com/academy/lesson/the-sensory-system-definition-parts-functions.html
 https://en.wikipedia.org/wiki/Sensory_nervous_system
 https://lifeeducationpoint.com/types-of-sensory-receptors/
 https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Anatomy_and_Physiology_(Bound
less)/12%3A_Peripheral_Nervous_System/12.2%3A_Sensory_Receptors/12.2A%3A__Classification_of
_Receptors_by_Stimulus