Topic 5: Nervous System III

Question 1

Brain/Spinal cord overview

Answer 1

• sensory (afferent) division “inputs” info into brain and spinal cord (control centres)
• brain + spinal cord integrate info and control effectors through motor (efferent) division (“output”).

Question 2

Spinal cord-reflexes

Answer 2

• rapid automatic, response to stimuli
• stimulus always causes the same motor response
• usually protective
• involve 2 or more neurons
• Reflex pathway or arc = pathway of impulses

Question 3

Reflex categorized according to:

Answer 3

• effector
• which sides of the body the senses and motor neurons are located
• number of synapses in arc

Question 4

Effector

Answer 4

• somatic reflex = effector is skeletal muscle

- visceral (autonomic) reflex = effector is smooth muscle, cardiac muscle, or glands

Question 5

Which sides of the body the sensory and motor neurons are located

Answer 5

• ipsilateral reflex = sensory and motor neurons are on the same side
• contralateral reflex = sensory + motor neurons are on opposite sides

Question 6

number of synapses (+ neurons) in arc

Answer 6

• monosynaptic reflex = one synapse between 1 sensory + 1 motor neuron
• polysynaptic reflex = 2 or more synapses between 3 or more neurons

Question 7

Stretch Reflex

e.g. knee jerk reflex

Answer 7

• extensor muscle contracts
• stimulus = tapping patellar ligament, which stretches the quadriceps femoris muscle
• receptor = muscle spindle (in quad.)
• effector = skeletal muscle (quad.) – it contracts
• ipsilateral, monosynaptic

Question 8

Flexor (Withdrawal) Reflex

e.g. in leg

Answer 8

• stimulus = stepping on nail
• receptor = touch, pressure, pain
• effector = hamstrings (= flexors) ⇒ contract
• ipsilateral, polysynaptic

Question 9

Crossed Extensor Reflex

e.g. in leg

Answer 9

• stimulus = stepping on nail
• receptor= touch, pressure, pain
• effector = quadriceps femoris in the opposite leg (= extensor) ⇒ contracts
• contralateral, polysynaptic
• keeps you from falling down when ii) occurs

Question 10

Reciprocal Inhibition

Answer 10

• skeletal muscle (or group) contracts (= agonist)
• at same time, antagonist prevented from contracting (inhibitory neurons firing)
  e. g. in stretch reflex
• quadriceps femoris (agonist) contracts
• hamstrings (antagonists) contraction inhibited

Question 11

Autonomic Spinal Reflexes

Answer 11

• Effector = smooth m., cardiac m., or glands
  e. g. Micturition Reflex – urinary bladder
• stimulus = stretch of the bladder
• receptor = stretch receptors in bladder wall
• CNS = sacral segment of spinal cord (PSNS)
• effector = detrusor muscle (wall of bladder) – contracts & internal urethral sphincter opens (both are smooth muscle)

Question 12

Brain

Answer 12

• Cerebrum
• Brain Stem
• Hypothalamus

Question 13

Cerebrum

Answer 13

• interpreting sensory info from general and special senses
• initiating and controlling skeletal muscle movement (motor areas and basal nuclei)
• memory, intellect, etc
• relaying info between different parts of the brain and/or spinal cord (association, commissural, + projection tracts)

Question 14

Brain Stem

Answer 14

• controls life-sustaining processes e.g. breathing, circulation
• if brain stem functional but higher centres damaged ⇒ alive but not aware, no conscious control
• parts: midbrain, pons, medulla oblongata

Question 15

Midbrain

Answer 15

auditory and visual reflexes ⇒ movement of eyes (vision), head and neck in response to visual/auditory stimuli

Question 16

Pons

Answer 16

functions with medulla to regulate breathing (pontine respiratory centres)

Question 17

Medulla oblongata

Answer 17

functional regions:

• decussation (crossing) of sensory + motor tracts
• autonomic vital reflex centres
• other non-vital areas – control swallowing, coughing, sneezing, vomiting, etc.

Question 18

decussation (crossing) of sensory + motor tracts

Answer 18

e.g. left brain controls right skel. muscles, receives sensory input from right side

Question 19

autonomic vital reflex centres

Answer 19

Respiratory Area
-drives breathing rate
Cardiovascular Centres
-cardiac centre – modifies heart rate
-vasomotor area – controls blood vessel diameter

Question 20

Hypothalamus Major Functions

Answer 20

• Regulates ANS (glands, smooth, and cardiac muscle)
• Regulates parts of endocrine system
• Regulates temperature - “thermostat cells”
• Regulates food + water intake, body fluid conc.
• Part of limbic system (composed of cerebrum, thalamus, hypothalamus) = emotional brain
• Part of the reticular activating (RAS), with the reticular formation in the brain stem, cortex, and thalamus
  
  • alerting function when awake
  • receives sensory input for awakening ⇒ sets sleep/awake cycles

All major homeostatic functions! ⇒ damage = loss of homeostasis