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