Topic 5: Nervous System 3

Question 1

Overview

Answer 1

• Sensory (afferent) division “inputs” info into brain + 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

Pathway of Impulses

Answer 3

Stimulus –> R –> CNS –> E (effector)

Question 4

Reflexes Are Categorized According to:

Answer 4

1) Effector
2) Which sides of the body the sensory + motor neurone are located
3) Number of synapses ( + neurons) in arc

Question 5

Effector (Reflexes Category)

Answer 5

1) Somatic reflex = effector is skeletal muscle

2) Visceral (autonomic) reflex = effector is smooth muscle, cardiac muscle or glands

Question 6

Which sides of the body the sensory + motor neurone are located (Reflexes Category)

Answer 6

1) Ipsilateral reflex = sensory + motor neurons are on same side
2) Contralateral = Sensory + motor neurone are on opposite sides

Question 7

Number of synapses ( + neurons) in arc (Reflexes Category)

Answer 7

1) Monosynaptic reflex = one synapse between 1 sensory + 1 motor neurons
2) Polysynaptic reflex = 2 or more synapses between 3 or more neurons

Question 8

Stretch Reflex Example (Somatic Spinal Reflex)

Answer 8

Example: Knee jerk reflex

• Extensor muscle contracts
• Stimulus = trapping patellar ligament, which stretched the quadriceps femurs muscle
• Receptor = muscle spindle (in quad.)
• Effector = Skeletal muscle (quad.) - it contracts
• Ipsilateral, Monosynaptic

Question 9

Flexor (withdrawal) Reflex Example (Somatic Spinal Reflexes)

Answer 9

Example: In leg

• Stimulus = stepping on nail
• Receptor = touch, pressure, pain
• Effector = hastrings (= flexors) - contract
• Ipsilateral, polysynaptic

Question 10

Crossed Extensor Reflex Example

Answer 10

Example: In leg

• Stimulus = stepping on nail
• Receptor = tough, pressure, pain
• Effector = quadriceps femoris in the opposite leg (= extensor) - contracts
• Contralateral, polysynaptic
• Keeps you from falling down when it occurs

Question 11

Reciprocal Inhibition

Answer 11

• Skeletal muscle (or group) contracts ( = agonist)
• At same time, antagonist prevented from contracting (inhibitory interneurons firing)
• Example: In stretch reflex
• Quadriceps femoris (agonist) contracts
• Hamstings (antagonists) contraction inhibited

Question 12

Autonomic Spinal Reflexes

Answer 12

• Effector = smooth m., cardiac m., or glands
• Eg. Micturition Reflex - Urinary Bladder
• Stimulus = stretch of the bladder
• Receptor = stretch receptors in bladder wall
• CNS = sacral segment of spinal cord (PSNS)
• Effector = detrusor (wall of bladder) contracts & internal urethral sphincter opens (both are smooth muscle)

Question 13

Cerebrum

Answer 13

• Interpreting sensory info from general and special senses
• Initiating & 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:
  1) Midbrain
  2) Pon
  3) 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:
  1) Decussation (crossing) of sensory + motor tracts
• E.g. left brain controls right skeleton. muscles, receives sensory input from right side
  2) Autonomic Vital reflex centres
  a) Respiratory area - drives breathing rate
  b) Cardiovascular Centre -
• cardiac area - modifies heart rate
• Vasomotor area - controls swallowing, vomiting, coughing, sneezing, etc
  c) Other, non-vital areas - control swallowing, vomiting, coughing, sneezing, etc

Question 18

Hypothalamus

Answer 18

Major Functions:

1) Regulates ANS (smooth & cardiac muscle, glands)
2) Reg. parts of endocrine system
3) Reg. temperature -“thermostat cells”
4) Regulates food+ water intake, body fluid conc.
5) Part of limbic system (cerebrum, thalamus, hypothalamus) = emotional brain -basic emotions reg. here
6) Part of the reticular activating system (RAS), with the reticular formation in brain stem, cortex + thalamus

Question 19

RAS

Answer 19

• Alerting function when awake

- Receives sensory input for awakening - sets sleep/wake cycles

Question 20

All major functions…

Answer 20

Damage = loss of homeostasis