Topic 5: Nervous System III Flashcards
Brain/Spinal cord overview
- 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”).
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
Reflex categorized according to:
- effector
- which sides of the body the senses and motor neurons are located
- number of synapses in arc
Effector
- somatic reflex = effector is skeletal muscle
- visceral (autonomic) reflex = effector is smooth muscle, cardiac muscle, or glands
Which sides of the body the sensory and motor neurons are located
- ipsilateral reflex = sensory and motor neurons are on the same side
- contralateral reflex = sensory + motor neurons are on opposite sides
number of synapses (+ neurons) in arc
- monosynaptic reflex = one synapse between 1 sensory + 1 motor neuron
- polysynaptic reflex = 2 or more synapses between 3 or more neurons
Stretch Reflex
e.g. knee jerk reflex
- 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
Flexor (Withdrawal) Reflex
e.g. in leg
- stimulus = stepping on nail
- receptor = touch, pressure, pain
- effector = hamstrings (= flexors) ⇒ contract
- ipsilateral, polysynaptic
Crossed Extensor Reflex
e.g. in leg
- 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
Reciprocal Inhibition
- 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
Autonomic Spinal Reflexes
- 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)
Brain
- Cerebrum
- Brain Stem
- Hypothalamus
Cerebrum
- 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)
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: midbrain, pons, 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:
- decussation (crossing) of sensory + motor tracts
- autonomic vital reflex centres
- other non-vital areas – control swallowing, coughing, sneezing, vomiting, etc.
decussation (crossing) of sensory + motor tracts
e.g. left brain controls right skel. muscles, receives sensory input from right side
autonomic vital reflex centres
Respiratory Area -drives breathing rate Cardiovascular Centres -cardiac centre – modifies heart rate -vasomotor area – controls blood vessel diameter
Hypothalamus Major Functions
- 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
