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Homeostasis and the Nervous System (The structure and function of the…
Homeostasis and the Nervous System
Homeostasis
Maintains the optimal conditions for enzyme and cell function within the body
The control of:
Blood Sugar level
Body Temperature
Controlled by nervous or chemical responses
The nervous system
The central nervous system: Spinal Cord and Brain
Peripheral nervous system: carries signals between receptors and the central nervous system
Stimulus → receptor → coordinator → effector → response
The structure and function of the nervous system
The conditions inside the body need to be carefully controlled
These conditions are controlled by nervous or chemical responses
Control systems
Cells have receptors which detect changes in the environment (Stimuli)
The coordination centre, including the central nervous system or pancreas which recieves signals from the receptors.
Effectors: things that react to responses from receptors, including muscles and glands.
Nerve Cells
Nerve cells (Neurons) are specialised cells designed to carry electrical signals within the nervous system
Types of neurones
Sensory: ones that send signals as a result of environmental changes
Relay: Carry signals over long distances between the central nervous system and the rest of the body
Motor: Control movement of muscles.
Structure of a nerve cell
The long fibre (axon) which is insulated by a fatty (myelin) sheath to reduce electrical interference. They are long so they can carry messages up and down the body.
branches (dendrons) which make dendrites at each end. These receive incoming impulses from other neurones.
Receptors
Receptors are groups of specialised cells which detect changes in the environment, and send electrical signals to nerves as a response to these changes
Sensory organs
Contain receptors which respond to specific stimuli
Skin: temperature, contact, pain
Tongue: chemicals in food
Nose: chemicals in the air
Eye: light intensity and wavelength
Ear, Sound loudness and frequency and head position (balance)
Effectors
Effectors are muscles or glands that produce an effect based on a nerve signal
Muscle contractions for movement
Muscle squeesing saliva out of salivary gland
Gland releasing a hormone into blood
Synapses
A synapse is the place where two nerves meet
An electrical impulse travelles along the axon of a nerve cell
This triggers the nerve ending of the cell to produce chemical signals (neurotransmitters)
The chemicals diffues across the gap in the synapse and bind to the receptors of the next nerve cell
Neurotransmitters only bind to specific receptors
Reflexes
An automatic, fast response to a stimulus, which minimises danger from possibly dangerous stimulus
Stimulus -> Receptor -> Sensory Neurone -> Relay Neurone -> Motor Neurone -> Effector -> Response
A nerve pathway followed by a reflex action is called a Reflex Arc
Reflex Example:
Receptor in skin detects sharp change in temperature
Sensory neurone sends electrical impulse to relay neurones in the spinal cord. They connect sensory neurones to motor neurones.
Motor neurone send impulse to effector
Effector causes muscle contraction
The Brain
The brain controlls complex behaviour
It is made up of billions of neurones, and different areas perform different functions
Areas of the brain
The Cerebrum: is split into two halves and highly folded, it controls high level functions such as speech, intelligent thought and social interaction.
the cerebellum: controls motor skills and coordination
The medulla: controls unconcious, automated tasks, i.e breathing
The hypothalamus: controls body temperature and water balance
Investigating The Brain
Modern scientific methods have enabled us to determine the function of different parts of the brain
Scientists have been able to determine the function of different parts of the brain by studying patients with damage to specific areas of the brain
Brain Damage
The most famous case of brain damage is that of Phineas Gage, who had an accident whilst laying a railway track, causing an iron rod to penetrate his skull
He survived the accident, but the damage to his brain caused a shift in his personality, which caused him to become antisocial
Doctors realised that this change in behavoir was because a specific part of his brain was damaged
Non invasive prosedures to investigate the brain
Electrical Stimulation: Involves measuring brain activity through electical activity in the neurons in specific parts of the brain, this allows doctors to investigate the brain's reaction to stimuli
MRI scans: and MRI scan uses magnetic fields to produce 2d images of cross sections of the brain
This can be used to observe changes in brain activity when the patient is shown specific stimuli
Brain surgery may be needed to remove tumours or fluids, but there is a high risk involved due to the comples structure of, and the number of blood vessels in the brain
