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Nervous System: Exercises neural control using fast-traveling electrochemical impulses. It provides the fastest means of communication between body parts.Endocrine System: Exercises chemical control through hormones acting as chemical messengers.
Stimulus: Information received by the nervous system regarding changes in the environment, either inside or outside the body.Response: The behavior, reaction, or action shown by a living organism as a result of a stimulus.Pathway of Transmission:
Example: Eating food involves identifying food (eyes), placing it on a plate (hands), using utensils, chewing, swallowing, and digesting—all performing in a coordinated sequence using different organs.
Cell Body (Cyton): The main part of the neuron containing the nucleus. It receives impulses from dendrites and passes them to the axon.Dendrons & Dendrites: Finger-like projections branching out from the cyton are called dendrons. Their fine branches are called dendrites, which end in knob-like structures called terminal knobs.Axon: The longest single extension projecting from the cyton. Its end splits into terminal branches ending in synaptic knobs.Myelin Sheath (Modulated Sheath): A spirally-coiled sheath of fatty substance surrounding the axon. It insulates the axon and speeds up the conduction of nerve impulses.Nodes of Ranvier: Regular constrictions (gaps) along the myelin sheath of the axon.
Afferent Process: Dendrites receive impulses from neighboring neurons and conduct them toward the cyton.Efferent Process: The axon and its terminal branches transmit impulses away from the cyton to the dendrites of neighboring neurons or directly to an effector organ.
A synapse is the point of contact between the terminal branches of the axon of one neuron and the dendrites of an adjacent neuron.The nerve impulse crosses this microscopic gap as a chemical message (using neurotransmitters like acetylcholine).
Nerve Fibres: These are individual axons (some can be over a meter long).Nerve: A bundle of nerve fibres wrapped together in a protective sheath of connective tissue (similar to an insulated electric cable containing multiple wires).
Receiving the Stimulus: Sensory cells (receptors) detect changes in the external or internal environment.Processing of Stimulus (Transduction): Receptors convert physical/chemical stimuli into electrical nerve impulses.Transmission: Receptors transmit these sensory impulses to the brain or spinal cord via sensory neurons.Interpretation: Interneurons in the brain or spinal cord interpret the sensory impulses and convert them into motor impulses (decisions/orders).Transferring the Response: Motor nerve fibres transfer the response from the CNS to the effector organs (muscles or glands), prompting them to act.
Central Nervous System (CNS)Peripheral Nervous System (PNS) (which includes the Autonomic Nervous System (ANS))
Protection: Protected by three membranes called meninges and enclosed in a bony skull cavity called the cranium.Matter Distribution:Outer layer: Gray matter (consisting mainly of neuron cell bodies/cytons).Inner layer: White matter (consisting of myelinated axons).The largest and most highly developed part of the brain.Divided into left and right halves called cerebral hemispheres.Its outer gray matter is highly folded into ridges called gyri and grooves called sulci to accommodate billions of neurons.Functions:Seat of intelligence, consciousness, willpower, reasoning, thinking, learning, memorizing, and emotions (love, hate, appreciation).Responsible for sensory perceptions (sight, hearing, taste, smell, touch, pain, pressure, and temperature).Known as the “little brain”, located at the back of the cerebrum and partly overlapped by it.Functions: Coordinates voluntary movements, controls voluntary muscles, and maintains body posture and balance during activities like walking, swimming, running, and jumping.The posterior-most part of the brain, also called the brain stem.Functions: Coordinates involuntary activities of visceral (internal) organs. Regulates heartbeat, breathing movements, swallowing, and peristaltic movements of the digestive tract.Note: Injury to the medulla oblongata is fatal and can cause immediate death.
Extends downward from the medulla of the brain through the neural canal of the vertebral column (which protects it) to the lumbar region.Matter Distribution (Reverse of the Brain):Inner region: H-shaped gray matter.Outer region: White matter.Functions:Controls all types of reflex actions (automatic, involuntary responses).Mediates involuntary activities like heartbeat, glandular secretions, and breathing.Conducts sensory impulses up to the brain and motor impulses down from the brain.
Cranial Nerves: 12 pairs of nerves that arise directly from the brain and supply the head region.Spinal Nerves: 31 pairs of nerves that arise from the spinal cord to supply the rest of the body (excluding the head). Every spinal nerve is a mixed nerve (carrying both sensory and motor fibres).
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Prepared by: learnloophq@gmail.com
Chapter: 07. Nervous System
CHAPTER 7: NERVOUS SYSTEM — CRASH COURSE REVISION MATERIAL
1. CONTROL AND COORDINATION
Multicellular organisms manage simultaneously occurring bodily processes through two main coordinating systems:
Stimulus and Response
What is Coordination?
Coordination is the normal control over the functioning of body tissues and organs at the correct speed and in the correct sequence simultaneously within physiological limits.
2. NEURONS (NERVE CELLS)
The neuron is the structural and functional unit of the nervous system. The human nervous system is composed of millions of neurons.
Key Structural Parts of a Neuron
Transmission Flow in a Neuron
3. SYNAPSE AND NERVES
The Synapse
Nerves
Types of Nerves
Based on the direction and type of impulses they conduct, nerves are categorized into three groups:
Nerve Type
Description / Composition
Example
Sensory Nerves
Contain only sensory nerve fibres; bring impulses from sense organs to the brain or spinal cord.
Optic nerve of the eye
Motor Nerves
Contain only motor nerve fibres; carry impulses from the brain or spinal cord to effector organs (muscles/glands).
Nerves supplying eye muscles and tongue muscles
Mixed Nerves
Contain both sensory and motor nerve fibres.
Nerves going to the lower jaw, face, neck, and salivary glands
4. MECHANISM OF NERVOUS COORDINATION
Nervous coordination progresses through five distinct steps:
5. THE HUMAN NERVOUS SYSTEM
The human nervous system is split into two major anatomical divisions:
6. CENTRAL NERVOUS SYSTEM (CNS)
The CNS integrates and processes incoming information, then sends instructions to effectors. It is made of the Brain and Spinal Cord.
A. The Brain
The brain is the supreme controlling center.
The brain is divided into three main parts:
1. Cerebrum
2. Cerebellum
3. Medulla Oblongata
B. The Spinal Cord
7. PERIPHERAL NERVOUS SYSTEM (PNS)
The PNS consists of all nerves branching out from the CNS to connect it to the rest of the body.
8. AUTONOMIC NERVOUS SYSTEM (ANS)
The ANS consists of paired chains of ganglia on either side of the vertebral column. It controls involuntary activities of internal visceral organs and smooth muscles (such as blood vessels and the digestive tract).
It is divided into two highly antagonistic (opposite-acting) systems:
Feature
Sympathetic Nervous System
Parasympathetic Nervous System
Structural Origin
Arises from the thoracic and lumbar regions of the spinal cord.
Arises from the brain, and the cervical and sacral regions of the spinal cord.
Ganglia Location
Ganglia form a chain running parallel and close to the spinal cord.
Ganglia lie close to or directly within the target organ.
Functional Effect
Has a stimulatory effect on body organs; prepares the body for action during adverse, stressful situations (“fight or flight”).
Has an inhibitory or calming effect; brings body activities back to normal resting states.
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