Introduction to the Nervous System

Question 1

What does the CNS consist of?

Answer 1

Cerebral Cortex (Cerebrum)
Cerebellum –Coordination and movement.
Brain Stem – Regulates vital functions.

Question 2

What does the peripheral nervous system functionally divide into?
E.g.s?

Answer 2

Nerves and ganglia OUTSIDE the brain and spinal cord
1) Somatic PNS – Controls motor and sensory functions for the body wall.
E.G. Skin (sensory neurone), skeletal muscles (motor neurone).
2) Autonomic Nervous System – Regulates function of viscera (organs).
E.G. Internal Organs, Smooth (involuntary) muscle, pupils, sweating.
Has sympathetic and parasympathetic arms.
Also called: Visceral PNS, Vegetative NS, Involuntary NS.

Question 3

Define the terms afferent and efferent as applied to axons, giving specific examples of
neurons in each category

Answer 3

Afferent Axons – Towards the CNS from the PNS.
E.G. Sensory neurones, both somatic and
autonomic.

Efferent Axons – Away from the CNS to the PNS.
E.G. Motor neurones, both somatic and
autonomic.

Interneurons – CNS neurones that synapse with
other CNS neurones within the brain and spinal
cord.

Question 4

Afferent vs Efferent?

Answer 4

Afferent = Arrive
Efferent = Exit

Question 5

5 main lobes of brain+ functions
Rough areas (slide 10, lecture 1)

Answer 5

Frontal= conscious decision making
Parietal= somatosensory cortex (sensory signals from body to brain) (temp, hairs etc)
Occiptal= visual cortex
Temporal lobe= one each side, auditory cortex, personality (fear, anxieties),
Cerebellum= balance, fine motor skills

Question 6

Label physical parts of brain

slide 11, lecture 1

Answer 6

-

Question 7

Cranial nerve

slide 12, lecture 1

Answer 7

Accessory XI also called Spinoaccessory nerve

Question 8

Meninges layers

slide 14, lecture 1

Answer 8

Dura mater= strong

Question 9

Where does the CNS end?

Answer 9

At the margins of the spinal cord.

The dorsal and ventral roots that emerge from the spinal cord are part of the PNS

Question 10

Types of cells in brain

Answer 10

Unipolar
Bipolar
Pseudounipolar
Multipolar

Question 11

Parts of cell in brain

Answer 11

Axon
Dendrite
Myelin Sheath

Question 12

How are axons arranged into nerves

Answer 12

Spinal nerves contain both afferent and efferent axons
They are bundled into fascicles surrounded by perineurium.
The whole nerve is in a tough epineurium capsule.
Individual axons are also wrapped with myelin and endoneurium, though some are unmyelinated, e.g. nociceptive (pain) neurons

Question 13

Cells other than neurons in the brain

Answer 13

These are all glial cells:
Microglia- immune cells
Astrocytes- form the blood-brain-barrier and recycle neurotransmitters
Oligodendrocytes (Schwann cells in PNS) produce myelin sheath

Question 14

Difference in regenerative capacity of PNS vs CNS

Answer 14

Axons in PNS can regenerate after injury
Injury leads to stimulation of phagocytes, which remove debris which would otherwise inhibit regrowth

Axons in CNS have limited regenerative capacity
Glia exert inhibitory influence on regeneration
Glial scars form in place of injured brain tissue

Question 15

Types of sensory perception pathways
Purpose
Description
Pathways
Travels up
Crossing Point
Damage Location
Draw diagram- picture 2

Answer 15

1) Dorsal column-medial lemniscus pathway
Conveys fine touch, vibration and two-point discrimination
Sensory afferents enter grey matter via the dorsal horn, travelling up the dorsal column to the medulla, where they synapse to a second order neurone that crosses and travels to the thalamus; here the second order synapses to a third order neurone

Pathways:
Skin to medulla (1st order) crossing
Medulla to thalamus (2nd order)
Thalamus to somatosensory (3rd order)

Travels up Dorsal column

Crossing point= Medulla (brainstem)

Below medulla = same side loss of sensation
Above medulla = opposite side loss of sensation

2) Spinothalamic pathway
Conveys pain and temperature sensation

Can damage dorsal column and still feel pain and temperature in affected limb
Sensory afferents enter the dorsal horn and immediately synapse to a second order neurone that crosses and travels on the contralateral side straight to the thalamus, synapsing to a third order there

Pathways:
Skin to dorsal horn (1st order) crossing
Dorsal horn to thalamus (2nd order)
Thalamus to somatosensory (3rd order)

Travels up Spinothalamic tract

Crossing point= Entry to the spinal cord

Outside cord = same side loss of sensation
Inside cord = opposite side loss of sensation

Question 16

Types of motor pathways
Purpose
Description
Pathways
Travels down
Crossing Point
Damage Location
Draw diagram- picture 2

Answer 16

1) Lateral Corticospinal Tract
Carries impulses from the motor cortex of the brain to skeletal muscles - consciously controlled
Neurones originating in the brain travel to the pyramids of the brainstem, where they cross and enter the corticospinal tracts, synapsing directly onto the motor neurones that control muscle activity

Pathways:
a) Motor cortex to anterior horn (upper motor neurone)
pyramidal decussation
corticospinal tract

b) Anterior horn to muscle (lower motor neurone)

Travels down Corticospinal tract

Crossing point= Pyramidal decussation in the medullary pyramid (brainstem)

Below medulla = same side loss of movement
Above medulla = opposite side loss of movement
Brain = contralateral loss of movement

2) Vestibulospinal Tract- DOESN’T CROSS OVER TO OTHER SIDE OF BODY
Receives input from ear’s vestibular system for orientation and balance
Creates microtwitches to maintain balance; entire tract is ipsilateral without crossing; neurones originating from the vestibular nuclei of the brainstem travel down the vestibulospinal tract to inhibitory or excitatory motor or intermediate neurones

Pathways:
Neurones originate from vestibular nuclei
Intermediate neurone (if inhibitory)
Excitatory neurones to extensor muscles, inhibitory neurones to flexor muscles

Travels down Vestibulospinal tract

NO CROSSING POINT

Ipsilateral to injury as no crossing