Human Anatomy and Physiology 1 - Chapter 7 and 8

1. Human Anatomy and
Physiology 1
DR. CHAMENDRA SIRIMANNA (M.B.B.S)

2. Full Content of Human anatomy and
physiology 1
1. Body Organization
2. The Cell
3. Tissues, Membranes, and Glands
4. Integumentary System
5. The Skeletal System
6. The Muscular System
7. The Nervous System
8. The Special Senses

3. The Nervous System
 The students should be able to explain the structure and function of muscle tissue and be able to relate the
neural, electrochemical, and physical events of muscle contractions to body movements.
 Specific Learning Outcomes:
 The Nervous System General Outcome: The understanding of the major divisions of the nervous system,
their component structures, and the various homeostatic mechanisms which operate under nervous
control. Which includes the general role of the nervous system, neuroglia and neurons, the specific
functions for the types of neuroglial cells, the specific functions of the parts of a neuron, an injured nerve
fiber may regenerate, the sequence of events involved in the initiation and conduction of a nerve impulse,
the all-or-none principle of impulse transmission and the factors that determine the rate of impulse
transmission by a neuron, the synapse and factors involved in the conduction of an impulse across a
synapse, the three coverings of the brain and spinal cord, the spinal cord and its relationship to the spinal
nerves, white matter, gray matter, nerves, ganglia, tracts, and nuclei, t reflex arc, the distributions of the 31
pairs of spinal nerves, the 12 cranial nerves, the peripheral nervous system the general functions of the
sympathetic and the parasympathetic divisions of the autonomic nervous system, the major parts of the
brain, the formation, circulation, and resorption of cerebrospinal fluid, blood supply to the brain, nervous
system disorders, and lastly the autonomic and somatic reflexes.

4. Nervous Tissue
 Both the nervous and endocrine systems have the same objective: to keep
controlled conditions within limits that maintain life.
 The nervous system regulates body activities by responding rapidly using
nerve impulses; the endocrine system responds by releasing hormones.
 The nervous system is also responsible for our perceptions, behaviors, and
memories, and it initiates all voluntary movements.
 Because this system is quite complex, we discuss its structure and function
in several.
 The lecture focuses on the organization of the nervous system and the
properties of neurons (nerve cells) and neuroglia (cells that support the
activities of neurons).

5. Overview of the Nervous system
 1. The central nervous system (CNS) consists of the brain and spinal cord.
 2. The peripheral nervous system (PNS) consists of all nervous tissue outside the CNS.
Components of the PNS include nerves and sensory receptors.
 3. The PNS is divided into a sensory (afferent) division and a motor (efferent) division.
 4. The sensory division conveys sensory input into the CNS from sensory receptors.
 5. The motor division conveys motor output from the CNS to effectors (muscles and glands)
 6. The efferent division of the PNS is further subdivided into a somatic nervous system
(conveys motor output from the CNS to skeletal muscles only) and an autonomic nervous
system (conveys motor output from the CNS to smooth muscle, cardiac muscle, and glands).
The autonomic nervous system in turn is divided into a sympathetic nervous system,
parasympathetic nervous system, and an enteric nervous system.
 7. The nervous system helps maintain homeostasis and integrates all body activities by
sensing changes (sensory function), interpreting them (integrative function), and reacting to
them (motor function).

8. Histology of
Nervous Tissue
 1. Nervous tissue consists of neurons (nerve cells) and
neuroglia. Neurons have the property of electrical excitability
and are responsible for most unique functions of the nervous
system: sensing, thinking, remembering, controlling muscle
activity, and regulating glandular secretions.
 2. Most neurons have three parts. The dendrites are the main
receiving or input region. Integration occurs in the cell body,
which includes typical cellular organelles. The output part
typically is a single axon, which propagates nerve impulses
toward another neuron, a muscle fiber, or a gland cell.
 3. Synapses are the site of functional contact between two
excitable cells. Axon terminals contain synaptic vesicles filled
with neurotransmitter molecules.
 4. Slow axonal transport and fast axonal transport are systems
for conveying materials to and from the cell body and axon
terminals.
 5. On the basis of their structure, neurons are classified as
multipolar, bipolar, or unipolar.

9. Histology of
Nervous Tissue
 6. Neurons are functionally classified as sensory (af erent)
neurons, motor (ef erent) neurons, and interneurons. Sensory
neurons carry sensory information into the CNS. Motor neurons
carry information out of the CNS to ef ectors (muscles and
glands). Interneurons are located within the CNS between
sensory and motor neurons.
 7. Neuroglia support, nurture, and protect neurons and maintain
the interstitial fluid that bathes them. Neuroglia in the CNS
include astrocytes, oligodendrocytes, microglial cells, and
ependymal cells. Neuroglia in the PNS include Schwann cells and
satellite cells.
 8. Two types of neuroglia produce myelin sheaths:
Oligodendrocytes myelinate axons in the CNS, and Schwann
cells myelinate axons in the PNS.
 9. White matter consists of aggregates of myelinated axons; gray
matter contains cell bodies, dendrites, and axon terminals of
neurons, unmyelinated axons, and neuroglia.
 10. In the spinal cord, gray matter forms an H-shaped inner core
that is surrounded by white matter. In the brain, a thin,
superficial shell of gray matter covers the cerebral and cerebellar
hemispheres.

10. The Spinal Cord and Spinal Nerves
 About 100 million neurons and even more neuroglia compose the spinal cord, the part of the central
nervous system that extends from the brain.
 The spinal cord and its associated spinal nerves contain neural circuits that control some of your most
rapid reactions to environmental changes.
 If you pick up something hot, the grasping muscles may relax and you may drop the hot object even
before you are consciously aware of the extreme heat or pain.
 This is an example of a spinal cord reflex—a quick, automatic response to certain kinds of stimuli that
involves neurons only in the spinal nerves and spinal cord.
 Besides processing reflexes, the gray matter of the spinal cord also is a site for integration (summing) of
excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs).
 These graded potentials arise as neurotransmitter molecules interact with their receptors at synapses in the
spinal cord.
 The white matter of the spinal cord contains a dozen major sensory and motor tracts, which function as the
“highways” along which sensory input travels to the brain and motor output travels from the brain to
skeletal muscles and other effectors.
 Recall that the spinal cord is continuous with the brain and that together they make up the central nervous
system (CNS).

11. Spinal Cord
Anatomy
 1. The spinal cord is protected by the vertebral column, the
meninges, cerebrospinal fluid, and denticulate ligaments.
 2. The three meninges are coverings that run continuously
around the spinal cord and brain. They are the dura mater,
arachnoid mater, and pia mater.
 3. The spinal cord begins as a continuation of the medulla
oblongata and ends at about the second lumbar vertebra
in an adult.
 4. The spinal cord contains cervical and lumbar
enlargements that serve as points of origin for nerves to
the limbs.
 5. The tapered inferior portion of the spinal cord is the
conus medullaris, from which arise the filum terminale and
cauda equina.

12. Spinal Cord
Anatomy
 6. Spinal nerves connect to each segment of the spinal cord
by two roots. The posterior or dorsal root contains sensory
axons, and the anterior or ventral root contains motor neuron
axons.
 7. The anterior median fissure and the posterior median
sulcus partially divide the spinal cord into right and left sides.
 8. The gray matter in the spinal cord is divided into horns,
and the white matter into columns. In the center of the spinal
cord is the central canal, which runs the length of the spinal
cord.
 9. Parts of the spinal cord observed in transverse section are
the gray commissure; central canal; anterior, posterior, and
lateral gray horns; and anterior, posterior, and lateral white
columns, which contain ascending and descending tracts.
Each part has specific functions.
 10. The spinal cord conveys sensory and motor information
by way of ascending and descending tracts, respectively.

15. Spinal Nerves
 1. The 31 pairs of spinal nerves are named and numbered according
to the region and level of the spinal cord from which they emerge.
There are 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5
pairs of sacral, and 1 pair of coccygeal nerves.
 2. Spinal nerves typically are connected with the spinal cord by a
posterior root and an anterior root. All spinal nerves contain both
sensory and motor axons (they are mixed nerves).
 3. Three connective tissue coverings associated with spinal nerves
are the endoneurium, perineurium, and epineurium.
 4. Branches of a spinal nerve include the posterior ramus, anterior
ramus, meningeal branch, and rami communicantes.
 5. The anterior rami of spinal nerves, except for T2–T12, form
networks of nerves called plexuses.
 6. Emerging from the plexuses are nerves bearing names that
typically describe the general regions they supply or the route they
follow.
 7. Anterior rami of nerves T2–T12 do not form plexuses and are
called intercostal (thoracic) nerves. They are distributed directly to
the structures they supply in intercostal spaces.
 8. Sensory neurons within spinal nerves and the trigeminal (V) nerve
serve specific, constant segments of the skin called dermatomes.
 9. Knowledge of dermatomes helps a physician determine which
segment of the spinal cord or which spinal nerve is damaged.

16. Spinal Cord
Physiology
 1. The white matter tracts in the spinal cord are highways for
nerve impulse propagation. Along these tracts, sensory input
travels toward the brain, and motor output travels from the
brain toward skeletal muscles and other effector tissues.
Sensory input travels along two main routes in the white
matter of the spinal cord: the posterior column and the
spinothalamic tract. Motor output travels along two main
routes in the white matter of the spinal cord: direct pathways
and indirect pathways.
 2. A second major function of the spinal cord is to serve as an
integrating center for spinal reflexes. This integration occurs
in the gray matter.
 3. A reflex is a fast, predictable sequence of involuntary
actions, such as muscle contractions or glandular secretions,
which occurs in response to certain changes in the
environment. Reflexes may be spinal or cranial and somatic
or autonomic (visceral).
 4. The components of a reflex arc are sensory receptor,
sensory neuron, integrating center, motor neuron, and
effector.

17. Spinal Cord
Physiology
 5. Somatic spinal reflexes include the stretch reflex, the tendon
reflex, the flexor (withdrawal) reflex, and the crossed extensor
reflex; all exhibit reciprocal innervation.
 6. A two-neuron or monosynaptic reflex arc consists of one
sensory neuron and one motor neuron. A stretch reflex, such as
the patellar reflex, is an example.
 7. The stretch reflex is ipsilateral and is important in maintaining
muscle tone.
 8. A polysynaptic reflex arc contains sensory neurons,
interneurons, and motor neurons. The tendon reflex, flexor
(withdrawal) reflex, and crossed extensor reflexes are examples.
 9. The tendon reflex is ipsilateral and prevents damage to
muscles and tendons when muscle force becomes too extreme.
The flexor reflex is ipsilateral and moves a limb away from the
source of a painful stimulus. The crossed extensor reflex extends
the limb contralateral to a painfully stimulated limb, allowing the
weight of the body to shif when a supporting limb is withdrawn.
 10. Several important somatic reflexes are used to diagnose
various disorders. These include the patellar reflex, Achilles
reflex, Babinski sign, and abdominal reflex.

18. The Autonomic Nervous System
 The motor (efferent) division of the peripheral nervous system (PNS) is
divided into a somatic nervous system (SNS) and autonomic nervous
system (ANS).
 The ANS usually operates without conscious control. However, centers in
the hypothalamus and brainstem do regulate ANS reflexes.
 In this lecture, we compare structural and functional features of the
somatic and autonomic nervous systems.
 Then we discuss the anatomy of the motor portion of the ANS and
compare the organization and actions of its two major parts, the
sympathetic and parasympathetic divisions.

19. Comparison of Somatic
and Autonomic Nervous
Systems
 1. The somatic nervous system operates under conscious
control; the ANS usually operates without conscious control.
 2. Sensory input for the somatic nervous system is mainly
from the somatic senses and special senses; sensory input
for the ANS is from interoceptors, in addition to somatic
senses and special senses.
 3. The axons of somatic motor neurons extend from the CNS
and synapse directly with an effector. Autonomic motor
pathways consist of two motor neurons in series. The axon
of the first motor neuron extends from the CNS and
synapses in an autonomic ganglion with the second motor
neuron; the second neuron synapses with an effector.
 4. The output (motor) portion of the ANS has two major
divisions: sympathetic and parasympathetic. Most body
organs receive dual innervation; usually one ANS division
causes excitation and the other causes inhibition. The
enteric division consists of nerves and ganglia within the
wall of the GI tract.
 5. Somatic nervous system effectors are skeletal muscles;
ANS ef ectors include cardiac muscle, smooth muscle, and
glands. 6. Table 15.1 compares the somatic and autonomic
nervous systems.

25. The Special Senses
 The general senses include somatic senses (tactile, thermal, pain, and proprioceptive)
and visceral sensations.
 Receptors for the general senses are scattered throughout the body and are relatively
simple in structure.
 They range from modified dendrites of sensory neurons to specialized structures
associated with the ends of dendrites.
 Receptors for the special senses— smell, taste, vision, hearing, and equilibrium—are
anatomically distinct from one another and are concentrated in specific locations in the
head.
 They are usually embedded in the epithelial tissue within complex sensory organs such
as the eyes and ears.
 Neural pathways for the special senses are also more complex than those for the
general senses.
 In this lecture we examine the structure and function of the special sense organs, and
the pathways involved in conveying their information to the central nervous system.

26. Olfaction: Sense
of Smell
 1. The receptors for olfaction, which are
bipolar neurons, are in the nasal epithelium
along with olfactory glands, which produce
mucus that dissolves odorants.
 2. In olfactory reception, a receptor potential
develops and triggers one or more nerve
impulses.
 3. The threshold of smell is low, and
adaptation to odors occurs quickly.
 4. Axons of olfactory receptor cells form the
olfactory (I) nerves, which convey nerve
impulses to the olfactory bulbs, olfactory
tracts, limbic system, and cerebral cortex
(temporal and frontal lobes).

27. Gustation:
Sensation of Taste
 1. The receptors for gustation, the gustatory
receptor cells, are located in taste buds.
 2. Dissolved chemicals, called tastants, stimulate
gustatory receptor cells by flowing through ion
channels in the plasma membrane or by binding
to receptors attached to G proteins in the
membrane.
 3. Receptor potentials developed in gustatory
receptor cells cause the release of
neurotransmitter, which can generate nerve
impulses in first-order sensory neurons.
 4. The threshold varies with the taste involved,
and adaptation to taste occurs quickly. 5.
Gustatory receptor cells trigger nerve impulses in
the facial (VII), glossopharyngeal (IX), and vagus
(X) nerves. Taste signals then pass to the medulla
oblongata, thalamus, and cerebral cortex (parietal
lobe).

28. Vision: An
Overview
 1. More than half of the sensory
receptors in the human body
are located in the eyes.
 2. The eyes are responsible for
the detection of visible light, the
part of the electromagnetic
spectrum with wavelengths
ranging from about 400 to 700
nm.

29. Accessory
Structures of the
Eyes
 1. Accessory structures of the
eyes include the eyebrows,
eyelids, eyelashes, lacrimal
apparatus, and extrinsic eye
muscles.
 2. The lacrimal apparatus
consists of structures that
produce and drain tears.

31. Anatomy of the
Eyeball
 1. The eye is constructed of three layers:
(a) fibrous tunic (sclera and cornea), (b)
vascular tunic (choroid, ciliary body, and
iris), and (c) retina.
 4. The retina consists of a pigmented
layer and a neural layer that includes a
photoreceptor layer, bipolar cell layer,
ganglion cell layer, horizontal cells, and
amacrine cells.
 5. The anterior cavity contains aqueous
humor; the vitreous chamber contains
the vitreous bod

33. Physiology of
Vision
 1. Image formation on the retina involves refraction of light rays by
the cornea and lens, which focus an inverted image on the fovea
centralis of the retina.
 2. For viewing close objects, the lens increases its curvature
(accommodation) and the pupil constricts to prevent light rays from
entering the eye through the periphery of the lens.
 3. The near point of vision is the minimum distance from the eye at
which an object can be clearly focused with maximum
accommodation.
 4. In convergence, the eyeballs move medially so they are both
directed toward an object being viewed.
 5. The first step in vision is the absorption of light by photopigments
in rods and cones and isomerization of cis-retinal. Receptor potentials
in rods and cones decrease the release of inhibitory neurotransmitter,
which induces graded potentials in bipolar cells and horizontal cells.
 6. Horizontal cells transmit inhibitory signals between photoreceptors
and bipolar cells; bipolar or amacrine cells transmit excitatory signals
to ganglion cells, which depolarize and initiate nerve impulses.
 7. Impulses from ganglion cells are conveyed into the optic (II) nerve,
through the optic chiasm and optic tract, to the thalamus. From the
thalamus, impulses for vision propagate to the cerebral cortex
(occipital lobe). Axon collaterals of retinal ganglion cells extend to the
midbrain and hypothalamus.

34. Hearing
 1. The external (outer) ear consists of the auricle, external auditory canal, and tympanic
membrane (eardrum).
 2. The middle ear consists of the auditory tube, ossicles, oval window, and round window.
 3. The internal (inner) ear consists of the bony labyrinth and membranous labyrinth. The
internal ear contains the spiral organ (organ of Corti), the organ of hearing.
 4. Sound waves enter the external auditory canal, strike the tympanic membrane, pass
through the ossicles, strike the oval window, set up waves in the perilymph, strike the
vestibular membrane and scala tympani, increase pressure in the endolymph, vibrate the
basilar membrane, and stimulate hair bundles on the spiral organ (organ of Corti).
 5. Hair cells convert mechanical vibrations into a receptor potential, which releases
neurotransmitter that can initiate nerve impulses in first-order sensory neurons.
 6. Sensory axons in the cochlear branch of the vestibulocochlear (VIII) nerve terminate in the
medulla oblongata. Auditory signals then pass to the inferior colliculus, thalamus, and
temporal lobes of the cerebral cortex.

37. Equilibrium
 1. The maculae of the utricle and
saccule detect linear acceleration or
deceleration and head tilt.
 2. The cristae in the semicircular ducts
detect rotational acceleration or
deceleration.
 3. Most vestibular branch axons of the
vestibulocochlear nerve enter the
brainstem and terminate in the
medulla and pons; other axons enter
the cerebellum.

38. Thank you
END OF CHAPTER 7 AND 8