The nervous system is the body’s fast communication network, detecting changes, processing information, and coordinating responses. Its two major divisions are the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord, which act as the main control and processing centers.
The peripheral nervous system includes the nerves that connect the central nervous system to muscles, glands, skin, and internal organs.
The peripheral nervous system has two main functional branches: the somatic nervous system and the autonomic nervous system. The somatic system carries voluntary motor commands to skeletal muscles and sensory information from the body to the central nervous system. The autonomic system regulates involuntary functions such as heart rate, digestion, breathing adjustments, and blood vessel diameter.
Reflex arcs show how the nervous system can produce a rapid response through a short pathway, often involving the spinal cord before the brain fully processes the event.
Key Facts
- Central nervous system = brain + spinal cord.
- Peripheral nervous system = cranial nerves + spinal nerves + sensory and motor pathways outside the CNS.
- Somatic nervous system controls voluntary skeletal muscle movement and carries conscious sensory information.
- Autonomic nervous system controls involuntary effectors such as smooth muscle, cardiac muscle, and glands.
- Reflex arc pathway: receptor -> sensory neuron -> spinal cord interneuron -> motor neuron -> effector.
- Nerve signal speed can be estimated with v = d/t, where v is speed, d is distance, and t is time.
Vocabulary
- Central nervous system
- The division of the nervous system made of the brain and spinal cord that processes information and coordinates responses.
- Peripheral nervous system
- The division of the nervous system made of nerves outside the brain and spinal cord that carry signals to and from the body.
- Somatic nervous system
- The peripheral division that controls voluntary skeletal muscles and carries sensory information from skin, muscles, and joints.
- Autonomic nervous system
- The peripheral division that regulates involuntary body functions such as heart rate, digestion, and gland activity.
- Reflex arc
- A rapid neural pathway that produces an automatic response to a stimulus, often through the spinal cord.
Common Mistakes to Avoid
- Calling all nerves part of the central nervous system is wrong because the CNS only includes the brain and spinal cord, while most body nerves belong to the PNS.
- Thinking the somatic nervous system controls only movement is incomplete because it also carries sensory information from the body to the CNS.
- Assuming autonomic actions are always completely independent of the brain is wrong because the brain can regulate and influence autonomic activity.
- Drawing a reflex arc as stimulus -> brain -> muscle is usually wrong for simple spinal reflexes because the spinal cord can coordinate the response before full conscious awareness.
Practice Questions
- 1 A sensory signal travels 1.5 m from a hand to the spinal cord in 0.03 s. What is the signal speed in m/s?
- 2 A reflex response takes 0.08 s after a stimulus. If the nerve pathway length is 2.4 m total, estimate the average signal speed using v = d/t.
- 3 Explain why pulling your hand away from a hot surface can happen before you consciously feel pain, and identify the major parts of the reflex arc involved.