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Chapter 13: Nervous System in Mammals
Students should be able to:
1. Outline the features of sensory neurons and relay neurons.2. 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 Components
13.1.2 The Motor Neurone
13.1.3 The Sensory Neurone
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Nervous System
Central Nervous System (CNS) Peripheral Nervous System (PNS)
Brain Spinal cord Spinal NervesCranial Nerves
Motor end plate
Serve as insulating layer
End of axon connection to the muscle fibre
Transmit impulses towards cell body
Fibres usually short
Transmit impulses away from cell body
Fibres usually long
Neurilemma Membrane that
surrounds the myelin sheath
Provides nourishment for the fibre
13.1.4 Relationship between the Sensory, Motor & Relay Neurones
13.2 The Mammalian Brain
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A gap between 2 connecting neurones impulses cross synapse by chemical means
13.2.1 Structure
Parts Components Structure Function
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Forebrain Cerebrum (1) Consists of 2 hemispheres
Largest part of the brain
Surface enlarged with deep grooves
Intelligence Memory Learning Overall control
of voluntary actions
EmotionsHypothalamu
s (2) Is the floor of
the cerebral hemisphere
Regulate body temperature
Regulate blood osmotic pressure
Control appetite, sleep & emotions
Pituitary gland (3)
A gland that is attached to the hypothalamus
Produces hormones (e.g. ADH)
Midbrain (4) Consists of optic lobes (4 small bodies)
Control visual reflexes (e.g. Movement of eyeballs)
Hindbrain Cerebellum (5)
Large Surface
thrown into many folds
Control muscular coordination
Body balance Medulla
oblongata (6) Lies below
cerebellum 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)o Muscle thus contracts under conscious control / will of the
person
13.3.2 Reflex actions A rapid action which does not involve conscious control Journey of impulses
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o Sensory receptors Relay Neurone (spinal cord) Effector (Muscles)
o Muscle thus suddenly contracts without conscious control / will of the person
13.3.3 Spinal cord Coordinate simple reflex action Provides a pathway for nerve impulses
o Into the brain from receptoro Out of the brain to effectors
13.3.4 The Reflex Arc
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 impulseo Receptor neurone + relay neurone (eg. spinal cord) + effector
neuroneo Effector (muscle or gland stimulated)
Types of reflexeso 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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From sense organ
Eg. To muscles
Dorsal Root
Ventral Root
13.3.5 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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StimulusResponse