Unit 8
Human Biology
Chapter 8.5
Nervous SystemClass 12 Biology – Nervous System Notes PDF
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Introduction
The human nervous system includes the central nervous system, peripheral nervous system and autonomic nervous system. Its fundamental functional cell is the neuron.
1. Structure of Neuron
A neuron consists mainly of a cell body, dendrites and axon. Dendrites usually receive signals, while the axon carries impulses away from the cell body.
Fig. 1 – Labelled Neuron
2. Nerve Impulse and Synapse
A nerve impulse is an electrochemical change that travels along the membrane of a neuron. At a synapse, the arriving impulse can cause release of neurotransmitter, which crosses the synaptic cleft and influences the next cell.
Fig. 2 – Chemical Synapse
3. Divisions of Nervous System
Fig. 3 – Classification of Human Nervous System
4. Human Brain
The brain is protected by the skull and meninges. Major regions include the cerebrum, diencephalon, cerebellum and brain stem.
Cerebrum
Largest region; involved in sensation, voluntary activity, memory, reasoning and higher functions.
Cerebellum
Coordinates muscle activity, posture and balance.
Medulla Oblongata
Controls several vital involuntary functions such as breathing and cardiovascular reflexes.
Hypothalamus
Important in homeostasis, autonomic control and endocrine regulation.
Fig. 4 – Simplified Human Brain
5. Spinal Cord
The spinal cord lies within the vertebral canal. It conducts impulses between brain and body and serves as an important centre for reflex actions.
6. Peripheral and Autonomic Nervous Systems
Somatic Nervous System
Connects the CNS with skeletal muscles and sensory receptors; important in voluntary actions.
Sympathetic Division
Generally prepares the body for demanding activity, such as increasing heart rate and redirecting blood flow.
Parasympathetic Division
Generally supports rest, digestion and energy conservation.
Autonomic Nervous System
Controls many involuntary functions of smooth muscle, cardiac muscle and glands.
7. Reflex Action and Reflex Arc
Fig. 5 – Reflex Arc
8. Quick Revision & Exam Points
- Draw and label a neuron.
- Explain transmission across a synapse.
- Classify the human nervous system.
- Draw and label the human brain.
- Write functions of cerebrum, cerebellum and medulla.
- Differentiate sympathetic and parasympathetic divisions.
- Define reflex action and explain a reflex arc.
- Neuron = functional unit of nervous system.
- Dendrites receive signals.
- Axon carries impulses away.
- CNS = brain + spinal cord.
- PNS links CNS with body.
- ANS controls involuntary activity.
- Reflex is rapid and automatic.
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