Neuroanatomy and Physiology

1. Neuroanatomy and physiology
VSR 605, VSR 606
Dr. Rekha Pathak
Senior scientist
Division of Surgery

2. •Neurons conduct impulses
•The passage of Action potential
•RMP of muscle and nerves: The resting membrane potential in
skeletal muscle cells is similar to that in neurons, i.e. −70 to −90
mV. Unlike nerve cells, where the resting membrane potential is
predominantly a result of K+ permeability, skeletalmuscle cell
resting membrane potential receives a significant contribution
from Cl− conductance. (structure of cell memberane protein
bilipid and stacked with protein molecules)
•Neurons are the most sensitive cells to change in pH, pCO2,pO2
and blood glucose levels
•Neurons are classified into

3. • Sensory neuron: cell body outside the CNS and function is to
conduct impulses from periphery to CNS (for eg. Irritative
impulses)
• Depends on the direction of the action potential (afferent /
efferent, so afferent cell bodies are outside the CNS)

4. Interneurons: completely within the CNS: pass impulses within the CNS to the
motor neuron network (very complex) (eg. Motor functions centrally
governed and glandular secretions)

5. • Motor neurons: cell body in the CNS
and axons in outside the CNS (muscle
movement)
• Motor neurons are classified into
UMN and LMN
• UMN: cell bodies in the cerebral
cortex or brain stem and axons
forming the descending fasciculi (long
tracts)
• The LMN: Cell bodies in the
brainstem/spinal cord and axons for
the motor fibers which innervate the
muscular structures.
• The clinical signs of UMN and LMN
are different
• It can be related with the fact that if
nerve cells are destroyed no
regeneration but it is possible if the
axon is destroyed.

6. •Axons and some
dendrites and its branches
are covered with a layer
of white fatty substance
known as myelin sheath.
Size of the fibres 0.5-20
microns
•The smallest axon has
very thin film of myelin
sheath so they are called
unmyelinated (because
the sheath is not visible by
staining)

7. • Slow nerve conduction in unmyelinated fiber
• 0.5M/SECOND in very small unmyelinated fiber
• 100m/second very large myelinated fiber
• Velicity increases approximately with the fuber dia in myelinated nerve
fiber and approx with the square root of fiber dia. In unmyelinated fiber
• In young ones after birth slow pick up several weeks after birth
• CD, allergic reactions ------destruction of myelin
• Axons outside the CNS have one more covering called endoneuriuim
above the myelin

8. •Nerve damage---if distal (may
regenerate)
•If cell body damages---does not
regenerate
•The degeneration may be ascending or
descending degeneration
•Nissils substance undergo chromatolysis
•The myelin is converted into lipid
droplets and aligned along the broken
axon
•The Schwann cells elongate and
interconnect with each other
•Axons grow and join
•Glial scarring in CNS prevents
regeneration

9. • Due to
– Trauma
– acute compression
• Signs & symptoms
– Loss of motor function
– Loss of sensory function
• Pathology
– Demyelination/axonal degeneration
– Disruption of the sensory/motor function of the injured nerve
– Remyelination with axonal regeneration
– Reinnervation of the sensory receptors & muscle end plates
• Degenerative changes
• Axonal injury
– Degenerative changes at proximal & distal end
• Anterograde degeneration (Wallerian Degeneration)
– Affecting the
» Injured neuron
» Neurons functionally connected to the injured neuron
– Transneural degeneration
» also degenerate neurons that synapses with the injured neuron
– Starts in 24 hours
Peripheral nerve injury

10. • Retrograde Degeneration
– Extends up to the first node of Ranvier proximal to the injury
– Changes in the dendritic tree
» the parent cell body & the part of the axon still attached
to the cell body
– Chromatolytic changes
– Swelling of the cell
– Displacement of the nucleus to periphery
» sometimes extruded out
– Fragmentation & reduction of Golgi apparatus
– Disappearance of neurofibrils

11. • Chromatolysis
• disintegration of the Nissl substance
– begins within 24 – 48 hours
– begins near the axon hillock & spreads to other parts
• occurs in certain infectious or degenerative diseases of the
nervous system
– poliomyelitis
– progressive muscular atrophy
• degree of chromatolysis depends on
– proximity of the site of injury to the nerve cell
• more in motor neurons
• Wallerian degeneration

13. • Reg. Rate of nerves
• 0.5-2.0 mm / day in canine. There is down growth of
neurobifibrils from the proximal portion of severed nerve (if
connected with other nerves and AP is there), then chances
of regeneration will be more.
• The nerve impulse: AP, RMP
• Thicker fibers carry faster impulse
• Synapse: one neuron joins the other/ effectors
• May transmit signals/ may block signals/ may change it from
single impulse to repetitive impulses
• Reduce the signals
• Integrate the impulses with other neuron
• Excitatory transmitter: hyperesthesis, hyperalgesia and
excessive motor responses visual and tactile stimuli

14. • Inhibitory transmitter: very important because CNS
continuously receives a barrage of stimuli from the
peripheral nerves . Inhibition plays a role in selecting
the imp. Signals at a particular set of circumstances
• Strychnine poisoning : muscular rigidity
• Sensory receptors
• They turn specific form of energy into nerve impulses
• Mechanoreceptors: touch, pressure, kinesthetic, sound
equilibrium, lung stretch, heart stretch
• Thermo receptors: heat and cold
• Chemoreceptor
• Pain , taste smell and oxygen tension in blood
• Electromagnetic radiations receptors; sight—Rods and
cones of eye

15. • Effectors
• Reflexes: myotactic or stretch reflex- knee jerk
• The antigravity muscles are responsible for muscle
tone
• Knee jerk: when patella is hammered the stifle goes
into extension
• Neuroglia
• Meninges
• Internal cavities of the brain
• CSF
• Hydrocephalous
• BBB

16. Choroid plexus; made of ependydymal
cells and responsible for the synthesis
of CSF

18. •Blood CSF barrier-----At the choroid plexus
•CSF brain barrier------- at the CSF
•BBB--- Is actually due to the pedicular processes of the astrocytes which
cover the capillaries of the CNS. These interposition of the glial cells
provides the selectivity of the entrance of materials into the CNS tissue.

19. The Blood –CSF barrier : is based on organization of the choroid
plexus its capillaries

20. •The CSF brain barrier: selectivity of the ependymal cells lining the ventricles
and ependymal cells lining the ventricles and the cerebral aqueduct and the
astrocytes adjacent to the ependyma.
•Certain regions are devoid of BBB like pineal body, optic recess of the third
ventricle, the saccular eminence of the hypophyseal stalk and posterior lobe of
hypophysis.

21. Blood supply•Cerebrum: Anterior , middle
and posterior cerebral
arteries
•Cerebellar: Anterior and
posterior cerebellar artery

22. • Important for the
clinician who does
cerebral angiograms
for diagnostic
purposes to
recognize the normal
vascular pattern
• Clinical sign with
sudden flaccid hemi-
paresis suggest an
acute vascular
accident

23. • Subdural hemorrhage (Video)

24. Venous drainage is from the Dural sinuses (vascular channels
within the structure of the Dura mater)

25. • Brain metabolism utilizes about 14 per cent of the total
oxygen consumption of the body
• Carbohydrate oxidation to glucose is the chief energy
source
• Autoregulation of blood flow to the CNS
• Autonomic system (sympathetic and parasympathetic)
• Co2 is dominant than O2
• When carbon dioxide partial pressure PCO2 increases in the
capillaries the BV dilate allow rapid blood flow to remove
the excess co2 and other metabolites which can lower the
Co2 back to normal
• In brain edema: Vasoconstriction is brought about by
hyperventillation and oxygenation at the tissue site
• This process reduces the blood flow to tissue and edema
subsides
• It should not be excessive otherwise problem occurs