BHSC 201
Systems Anatomy & Physiology
The Nervous System
Basic Health Sciences (BHSC) Program
Academic Year 2024–2025
, 1. Overview of the Nervous System
The nervous system is the body's primary control and communication system. It detects
stimuli, processes information, and coordinates responses throughout the body.
1.1 Divisions of the Nervous System
Central Nervous System (CNS):
• Brain: cerebrum, cerebellum, brainstem
• Spinal cord: 31 segments; relays signals between brain and body
Peripheral Nervous System (PNS):
• Somatic nervous system: voluntary control of skeletal muscle
• Autonomic nervous system (ANS): involuntary control of organs
• ANS subdivisions: sympathetic (‘fight or flight’) and parasympathetic (‘rest and
digest’)
2. Neuron Physiology
2.1 Resting Membrane Potential
At rest, the inside of a neuron is approximately −70 mV relative to the outside. This is
maintained by:
• Na+/K+ ATPase: pumps 3 Na+ out and 2 K+ in
• K+ leak channels: K+ diffuses out, making the inside more negative
• Large negatively charged proteins trapped inside the cell
2.2 Action Potential
1. Depolarization: Na+ channels open; Na+ rushes in; membrane potential rises to
+30 mV
2. Repolarization: Na+ channels inactivate; K+ channels open; K+ flows out
3. Hyperpolarization: membrane briefly goes below −70 mV (undershoot)
4. Refractory period: neuron cannot fire again immediately (absolute refractory
period)
Systems Anatomy & Physiology
The Nervous System
Basic Health Sciences (BHSC) Program
Academic Year 2024–2025
, 1. Overview of the Nervous System
The nervous system is the body's primary control and communication system. It detects
stimuli, processes information, and coordinates responses throughout the body.
1.1 Divisions of the Nervous System
Central Nervous System (CNS):
• Brain: cerebrum, cerebellum, brainstem
• Spinal cord: 31 segments; relays signals between brain and body
Peripheral Nervous System (PNS):
• Somatic nervous system: voluntary control of skeletal muscle
• Autonomic nervous system (ANS): involuntary control of organs
• ANS subdivisions: sympathetic (‘fight or flight’) and parasympathetic (‘rest and
digest’)
2. Neuron Physiology
2.1 Resting Membrane Potential
At rest, the inside of a neuron is approximately −70 mV relative to the outside. This is
maintained by:
• Na+/K+ ATPase: pumps 3 Na+ out and 2 K+ in
• K+ leak channels: K+ diffuses out, making the inside more negative
• Large negatively charged proteins trapped inside the cell
2.2 Action Potential
1. Depolarization: Na+ channels open; Na+ rushes in; membrane potential rises to
+30 mV
2. Repolarization: Na+ channels inactivate; K+ channels open; K+ flows out
3. Hyperpolarization: membrane briefly goes below −70 mV (undershoot)
4. Refractory period: neuron cannot fire again immediately (absolute refractory
period)
