Notes
Structure and signaling
- The CNS is the brain and spinal cord; the PNS has sensory and motor divisions (somatic and autonomic: sympathetic and parasympathetic).
- Neurons have dendrites, a cell body and an axon. Myelin speeds conduction. Resting potential is about -70 mV.
- An action potential is all-or-none: threshold, depolarization by Na+ entering, repolarization by K+ leaving. At chemical synapses, calcium triggers neurotransmitter release.
Brain, cord and reflexes
- Cerebral lobes: frontal, parietal, temporal, occipital. Thalamus relays; hypothalamus maintains homeostasis; medulla controls heart and breathing; cerebellum coordinates movement.
- Reflex arc: receptor, sensory neuron, integration center, motor neuron, effector. Reflexes are rapid and involuntary.
Senses
- Eye: light passes through cornea, pupil and lens to the retina (rods and cones). Ear: eardrum, ossicles, cochlea for hearing; semicircular canals for balance.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Potassium channels open and K+ flows out, restoring the negative inside.
Broca's area in the frontal lobe controls speech production.
Action potentials are all-or-none; intensity is coded by frequency.
The primary somatosensory cortex in the parietal lobe processes touch.
Rods are sensitive to low light but do not detect color.
Blocking parasympathetic ("rest and digest") input leaves sympathetic effects dominant.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A cyclist touches a sharp thorn while riding. Her hand pulls back immediately, and a second later she feels pain and looks at her hand.
(a) Describe the pathway of the reflex that pulls her hand back, in order.
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A pain receptor in the skin sends an impulse along a sensory neuron to the spinal cord (integration center). An interneuron connects to a motor neuron, which carries the impulse to the effector, the muscles that withdraw the hand.
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(b) Explain why she felt the pain after the hand had already moved.
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The reflex is processed in the spinal cord without waiting for the brain. Meanwhile, sensory signals also travel up to the brain, which takes longer, so pain perception occurs later.
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(c) Describe what happens at the synapse between the sensory and the next neuron.
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The action potential arrives at the axon terminal, calcium channels open, and vesicles release neurotransmitter into the synaptic cleft. The transmitter binds receptors on the next neuron and opens ion channels, creating a new signal.
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