Topic 8: Grey Matter
Nervous and Hormonal Communication
How the nervous system works
• The nervous system detects changes in our environment (known as stimuli) through cells
called receptors.
• Receptors are sensitive to a number of different aspects of our environment, such as light,
pressure (touch) and chemicals in the air (smell).
• When receptors detect certain stimuli, they signal to the central nervous system (CNS)
through initiating an electrical impulse through a neuron (nerve cell).
• The neuron which sends an electrical impulse from the receptor within the sense organ and
the coordination centre is called the sensory neuron.
• The coordination centre receives impulses from various receptors around the body,
processes the information and coordinates a response by signalling to other parts of the body.
Coordination centres include the brain, spinal cord and pancreas.
• These organs will signal to an effector (a muscle or gland) by releasing an electrical impulse
along a motor neuron.
• Stimulation of an effector will produce a response such as muscle contraction or hormonal
release.
, How the hormonal system works
• The endocrine (hormonal) system is a group of glands, which secrete chemicals called
hormones.
• Glands secrete hormones when they are stimulated by neurons or by a change in
concentration of a chemical substance (such as another hormone).
• Hormones travel around our body in our bloodstream to their target organs where it
produces an effect.
• Target cells possess complementary receptors on their cell surface membranes that allow it
to respond to the hormone, triggering a response inside the cell.
• Hormones can be proteins/peptides e.g. insulin or steroids (a type of lipid) e.g. testosterone.
• Compared to the nervous system, the endocrine system is:
o Slower to bring about an effect
o Longer-lasting
o Widespread response (can act on multiple target tissues)
o Involves the use of chemicals rather than electrical impulses
Receptors
Our nervous system uses receptors to detect stimuli (changes in the environment) and pass on this
information to the CNS. Receptors can either be whole cells (e.g. photoreceptors are cells which are
sensitive to light) or proteins molecules which are found on the cell surface membrane. Each
receptor is specific to a single type of stimulus, such as light, temperature or glucose concentration.
When a receptor is not stimulated, there is a charge difference between the inside and outside of the
membrane and it is said to be polarised. When the receptor detects a stimulus, the permeability of
its cell membrane changes which changes the charge difference (potential difference) across the
membrane. If the change in potential difference is large enough (i.e. it exceeds the threshold level), it
will trigger an action potential (an electrical impulse) in a sensory neuron.
We contain the following receptors in our sense organs:
• Chemoreceptors - receptors which detect chemicals
• Thermoreceptors - receptors which detect heat
• Mechanoreceptors - receptors which detect pressure (see the Pacinian corpuscle below)
• Photoreceptors - receptors which detect light (e.g. rods and cones)
Nervous and Hormonal Communication
How the nervous system works
• The nervous system detects changes in our environment (known as stimuli) through cells
called receptors.
• Receptors are sensitive to a number of different aspects of our environment, such as light,
pressure (touch) and chemicals in the air (smell).
• When receptors detect certain stimuli, they signal to the central nervous system (CNS)
through initiating an electrical impulse through a neuron (nerve cell).
• The neuron which sends an electrical impulse from the receptor within the sense organ and
the coordination centre is called the sensory neuron.
• The coordination centre receives impulses from various receptors around the body,
processes the information and coordinates a response by signalling to other parts of the body.
Coordination centres include the brain, spinal cord and pancreas.
• These organs will signal to an effector (a muscle or gland) by releasing an electrical impulse
along a motor neuron.
• Stimulation of an effector will produce a response such as muscle contraction or hormonal
release.
, How the hormonal system works
• The endocrine (hormonal) system is a group of glands, which secrete chemicals called
hormones.
• Glands secrete hormones when they are stimulated by neurons or by a change in
concentration of a chemical substance (such as another hormone).
• Hormones travel around our body in our bloodstream to their target organs where it
produces an effect.
• Target cells possess complementary receptors on their cell surface membranes that allow it
to respond to the hormone, triggering a response inside the cell.
• Hormones can be proteins/peptides e.g. insulin or steroids (a type of lipid) e.g. testosterone.
• Compared to the nervous system, the endocrine system is:
o Slower to bring about an effect
o Longer-lasting
o Widespread response (can act on multiple target tissues)
o Involves the use of chemicals rather than electrical impulses
Receptors
Our nervous system uses receptors to detect stimuli (changes in the environment) and pass on this
information to the CNS. Receptors can either be whole cells (e.g. photoreceptors are cells which are
sensitive to light) or proteins molecules which are found on the cell surface membrane. Each
receptor is specific to a single type of stimulus, such as light, temperature or glucose concentration.
When a receptor is not stimulated, there is a charge difference between the inside and outside of the
membrane and it is said to be polarised. When the receptor detects a stimulus, the permeability of
its cell membrane changes which changes the charge difference (potential difference) across the
membrane. If the change in potential difference is large enough (i.e. it exceeds the threshold level), it
will trigger an action potential (an electrical impulse) in a sensory neuron.
We contain the following receptors in our sense organs:
• Chemoreceptors - receptors which detect chemicals
• Thermoreceptors - receptors which detect heat
• Mechanoreceptors - receptors which detect pressure (see the Pacinian corpuscle below)
• Photoreceptors - receptors which detect light (e.g. rods and cones)
