Chapter 13 Nervous System In Mammals - Lecture Notes

Chapter 13: Nervous System in Mammals Students should be able to: 1. 2.

Outline the features of sensory neurons and relay neurons. Discuss the function of the brain and spinal cord in producing a coordinated response as a result of a specific stimulus (reflex action).

13.1 The Mammalian Nervous System 13.1.1

13.1.2

Nervous System

Components

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

Brain

Cranial Nerves

Spinal cord

The Motor Neurone

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Transmit impulses towards cell body Fibres usually short

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Spinal Nerves

End of axon connection to the muscle fibre Motor end plate

Neurilemma • Membrane that surrounds the myelin sheath • Provides nourishment for the fibre

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Serve as insulating layer

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Transmit impulses away from cell body Fibres usually long

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13.1.3

The Sensory Neurone

13.1.4

Relationship between the Sensory, Motor & Relay Neurones A gap between 2 connecting neurones  impulses cross synapse by chemical means

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13.2 The Mammalian Brain 13.2.1

Structure

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Parts Forebrain

Components Cerebrum (1)

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Hypothalamus (2)

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Structure Consists of 2 hemispheres Largest part of the brain Surface enlarged with deep grooves Is the floor of the cerebral hemisphere

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Pituitary gland (3)

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Midbrain (4)

Hindbrain

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Cerebellum (5)

Medulla oblongata (6)

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A gland that is attached to the hypothalamus Consists of optic lobes (4 small bodies)

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Large Surface thrown into many folds Lies below cerebellum

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Function Intelligence Memory Learning Overall control of voluntary actions Emotions Regulate body temperature Regulate blood osmotic pressure Control appetite, sleep & emotions Produces hormones (e.g. ADH) Control visual reflexes (e.g. Movement of eyeballs) Control muscular coordination Body balance Controls involuntary actions such as Heartbeat Peristalsis Contraction / dilation of blood vessels

13.3 Spinal Cord & Spinal Nerves 13.3.1

Voluntary actions • An action which involves the conscious control of the brain • Journey of impulses o Brain  Relay Neurone (spinal cord)  Effector (Muscles)

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o Muscle thus contracts under conscious control / will of the person

13.3.2

13.3.3

13.3.4

Reflex actions • A rapid action which does not involve conscious control • Journey of impulses o Sensory receptors  Relay Neurone (spinal cord)  Effector (Muscles) o Muscle thus suddenly contracts without conscious control / will of the person Spinal cord • Coordinate simple reflex action • Provides a pathway for nerve impulses o Into the brain from receptor o Out of the brain to effectors The Reflex Arc Dorsal Root

From sense organ

Eg. To muscles

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Ventral Root Reflex Arc: The shortest pathway by which impulses travel from the receptor to effector in a reflex action Consists of: o Receptors  stimulated to generate impulse o Receptor neurone + relay neurone (eg. spinal cord) + effector neurone o Effector (muscle or gland stimulated) Types of reflexes o Spinal  controlled by spinal cord (e.g. knee jerk) o Cranial  controlled by reflex centers in the brain (e.g eye blinking reflex)

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• Stimulus

13.3.5

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Response

Conditioned Reflex Action Occurs as a result of past experiences of learning with a stimulus that was originally not effective in producing a response

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