Unit 9
Human Regulation and Reproduction
The Nervous System
The function of the nervous system is to detect internal and external environmental changes for our physical
safety and survival. The nervous system monitors all functions of the body. It receives information from inside
and outside the body and then sends signals to the appropriate organs in the body in direct response to this
information.
The central nervous system has two main organs: the brain
and the spinal cord. The peripheral nervous system has
sensory nerve cells that send information to the central
nervous system from external stimuli or internal organs,
and motor nervous system cells that carry information to
organs, muscles and glands from the central nervous
system.
The nervous system can be divided into the somatic nervous system and autonomic nervous system.
• The somatic nervous system is referred to as the voluntary nervous system because many of its actions
are under conscious control – it includes sensory neurons, which transmit impulses to the muscles.
• The autonomic nervous system controls involuntary responses, for example, contraction in the heart,
digestion, heart rate, breathing, salivation, and bladder.
The autonomic system has two distinct parts:
• The parasympathetic nervous system, which maintains the body’s functions on a day-to-day basis. It
is responsible for bringing the body back to a state of equilibrium. It slows the heart rate and decreases
the release of hormones into the bloodstream. It calms the body after a crisis and re-establishes
homeostasis. It can constrict the lungs to slow breathing and reduce the heartbeat.
• The sympathetic nervous system, which prepares the body to react in emerging situations.
Sympathetic nerve impulses can increase heart rate, constrict arteries to increase blood pressure, or
dilate pupils to increase sensory input from the eyes.
Voluntary and involuntary stimulation
Being able to respond to changes in our environment is essential to our safety and survival. It is the function of
the nervous system to enable us to detect changes and coordinate actions in response to these changes.
The nervous system enables us to respond to changes by:
• Detecting changes (stimuli) inside the body and in the external environment.
• Interpreting the change and deciding how to respond to it.
• Coordinating actions or behaviours that bring about a response to the change, such as moving away
from something dangerous.
Voluntary response – a conscious action taken in response to a stimulus (change in the environment) involuntary
response (reflex action) – not under conscious control, an involuntary and nearly instantaneous movement in
response to a stimulus, such as coughing and blinking etc.
, The structure of a sensory neuron and a motor neuron:
Diagram of a reflex arc:
The functions of sensory and motor neurones:
Sensory neurons are found in receptors such as the eyes, ears, tongue and skin, and carry nerve impulses to the
spinal cord and brain (CNS). When these nerve impulses reach the brain, they are converted into sensations such
as vision, hearing, taste and touch. Sensory neurons are afferent as they carry signals from a stimulus to the
spinal cord.
Relay neurons (interneuron) are found between sensory input and motor output/response. Relay neurons are
found in the brain and spinal cord and allow sensory and motor neurons to communicate.
Motor neurons are found in the central nervous system (CNS) and control muscle movements. When motor
neurons are stimulated, they release neurotransmitters that bind to the receptors on muscles to trigger a response,
which leads to movement. Motor neurons are efferent nerve fibres that carry signals away from the spinal cord
to the effector (mainly muscles or glands).
The function and structure of parts of sensory and motor neurons:
Cell body - Contains the nucleus, mitochondria, ribosomes and much of the cytoplasm (the area between the
nucleus and the cell membrane), most of the metabolic activity of the cell, including the generation of ATP
(Adenine Triphosphate Compound that stores energy) and synthesis of protein.
Dendrites - Short branch extensions spreading out from the cell body. Dendrites receive stimulus (action
potentials) and carry impulses from the environment or from other neurons carry them toward the cell body
Human Regulation and Reproduction
The Nervous System
The function of the nervous system is to detect internal and external environmental changes for our physical
safety and survival. The nervous system monitors all functions of the body. It receives information from inside
and outside the body and then sends signals to the appropriate organs in the body in direct response to this
information.
The central nervous system has two main organs: the brain
and the spinal cord. The peripheral nervous system has
sensory nerve cells that send information to the central
nervous system from external stimuli or internal organs,
and motor nervous system cells that carry information to
organs, muscles and glands from the central nervous
system.
The nervous system can be divided into the somatic nervous system and autonomic nervous system.
• The somatic nervous system is referred to as the voluntary nervous system because many of its actions
are under conscious control – it includes sensory neurons, which transmit impulses to the muscles.
• The autonomic nervous system controls involuntary responses, for example, contraction in the heart,
digestion, heart rate, breathing, salivation, and bladder.
The autonomic system has two distinct parts:
• The parasympathetic nervous system, which maintains the body’s functions on a day-to-day basis. It
is responsible for bringing the body back to a state of equilibrium. It slows the heart rate and decreases
the release of hormones into the bloodstream. It calms the body after a crisis and re-establishes
homeostasis. It can constrict the lungs to slow breathing and reduce the heartbeat.
• The sympathetic nervous system, which prepares the body to react in emerging situations.
Sympathetic nerve impulses can increase heart rate, constrict arteries to increase blood pressure, or
dilate pupils to increase sensory input from the eyes.
Voluntary and involuntary stimulation
Being able to respond to changes in our environment is essential to our safety and survival. It is the function of
the nervous system to enable us to detect changes and coordinate actions in response to these changes.
The nervous system enables us to respond to changes by:
• Detecting changes (stimuli) inside the body and in the external environment.
• Interpreting the change and deciding how to respond to it.
• Coordinating actions or behaviours that bring about a response to the change, such as moving away
from something dangerous.
Voluntary response – a conscious action taken in response to a stimulus (change in the environment) involuntary
response (reflex action) – not under conscious control, an involuntary and nearly instantaneous movement in
response to a stimulus, such as coughing and blinking etc.
, The structure of a sensory neuron and a motor neuron:
Diagram of a reflex arc:
The functions of sensory and motor neurones:
Sensory neurons are found in receptors such as the eyes, ears, tongue and skin, and carry nerve impulses to the
spinal cord and brain (CNS). When these nerve impulses reach the brain, they are converted into sensations such
as vision, hearing, taste and touch. Sensory neurons are afferent as they carry signals from a stimulus to the
spinal cord.
Relay neurons (interneuron) are found between sensory input and motor output/response. Relay neurons are
found in the brain and spinal cord and allow sensory and motor neurons to communicate.
Motor neurons are found in the central nervous system (CNS) and control muscle movements. When motor
neurons are stimulated, they release neurotransmitters that bind to the receptors on muscles to trigger a response,
which leads to movement. Motor neurons are efferent nerve fibres that carry signals away from the spinal cord
to the effector (mainly muscles or glands).
The function and structure of parts of sensory and motor neurons:
Cell body - Contains the nucleus, mitochondria, ribosomes and much of the cytoplasm (the area between the
nucleus and the cell membrane), most of the metabolic activity of the cell, including the generation of ATP
(Adenine Triphosphate Compound that stores energy) and synthesis of protein.
Dendrites - Short branch extensions spreading out from the cell body. Dendrites receive stimulus (action
potentials) and carry impulses from the environment or from other neurons carry them toward the cell body
