Topic 5: Nervous System 3 Flashcards
Overview
- Sensory (afferent) division “inputs” info into brain + spinal cord (control centres)
- Brain + spinal cord integrate info and control effectors through motor (efferent) division “output”
Spinal Cord Reflexes
- 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
Pathway of Impulses
Stimulus –> R –> CNS –> E (effector)
Reflexes Are Categorized According to:
1) Effector
2) Which sides of the body the sensory + motor neurone are located
3) Number of synapses ( + neurons) in arc
Effector (Reflexes Category)
1) Somatic reflex = effector is skeletal muscle
2) Visceral (autonomic) reflex = effector is smooth muscle, cardiac muscle or glands
Which sides of the body the sensory + motor neurone are located (Reflexes Category)
1) Ipsilateral reflex = sensory + motor neurons are on same side
2) Contralateral = Sensory + motor neurone are on opposite sides
Number of synapses ( + neurons) in arc (Reflexes Category)
1) Monosynaptic reflex = one synapse between 1 sensory + 1 motor neurons
2) Polysynaptic reflex = 2 or more synapses between 3 or more neurons
Stretch Reflex Example (Somatic Spinal Reflex)
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
Flexor (withdrawal) Reflex Example (Somatic Spinal Reflexes)
Example: In leg
- Stimulus = stepping on nail
- Receptor = touch, pressure, pain
- Effector = hastrings (= flexors) - contract
- Ipsilateral, polysynaptic
Crossed Extensor Reflex Example
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
Reciprocal Inhibition
- 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
Autonomic Spinal Reflexes
- 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)
Cerebrum
- 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)
Brain Stem
- 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
Midbrain
- Auditory and visual reflexes - movement of eyes (vision), head and neck in response to visual/auditory stimuli
Pons
- Functions with medulla to regulate breathing (pontine respiratory centres)
Medulla Oblongata
- 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
Hypothalamus
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
RAS
- Alerting function when awake
- Receives sensory input for awakening - sets sleep/wake cycles
All major functions…
Damage = loss of homeostasis
