- Created by: Rach2014
- Created on: 05-12-16 11:19
The Nervous System
The nervous system is split into two systems,
The Central Nervous System - this is the brain and spinal cord, and controls commands and decisions in the body.
The Peripheral Nervous System - this sends information to the CNS and transmits information from the CNS to muscles and glands to tell them what to do.
The Brain and Spinal Cord (CNS)
The central nervous system is made up of the brain and spinal cord:
The brain is split into two hemispheres and is the centre of out conscious awareness and thought. The brain's outer layer, the cerebral cortex, is highly developed in humans and is what separates us from other animals.
The spinal cord, an extension of the brain, is responsible for reflex actions such as moving away from something hot.
The Peripheral Nervous System
The PNS is the system that sends messages between the outside world to the CNS, and the CNS to the muscles and glands. It is made up of:
The Somatic Nervous System - this sends information from the receptor cells in the sense organs to the CNS, and messages from the CNS to the muscles.
The Autonomic Nervous System - this transmits information between internal organs. The system is automatic as it act involuntarily, for example it controls breathing. It is made up of the sympathetic and the parasympathetic nervous systems.
The Endocrine System
The endocrine system controls vital functions in the body,
Glands in the body, such as the adrenal glands, produce hormones which are released into the bloodstream and affect the cells that have receptors for that particular hormone.
Hormones can have very powerful effects on the body, for example, the thyroid gland produces the hormone thyroxine which increases the heart rate and increases metabolic rates.
The pituitary gland is the major gland in the endocrine system - it is located in the brain and controls the release of hormones from all other endocrine glands in the body.
The Fight or Flight Response
The fight or flight response is when the endocrine system and the autonomic nervous system work together to respond to threats. When a threat is sensed,
First, the hypothalamus triggers the autonomic nervous system,
The autonomic nervous system's state changes from the parasympathetic state to the sympathetic state,
Adrenaline, the stress hormone, is released from the adrenal medulla into the bloodstream, which prepares the body for fighting or running away,
Psychological changes can result in the person feeling sick (this is called having 'butterflies'),
Once the threat has passed, the parasympathetic state is activated - this returns the body to its resting state, and is sometimes referred to as the 'rest and digest' response.
There are three types of neurons:
Sensory neurons - these carry messages from the PNS to the CNS. They have long dendrites and short axons.
Motor neurons - these connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons.
Relay neurons - these connect the sensory neurons to the motor and other relay neurons. They have short dendrites and short axons.
The Structure of a Neuron
All neurons share the same basic structure:
The Cell Body, containing the nucleus, containing the genetic information of the cell.
Dendrites are connected to the cell body and carry nerve impulses from the neurons towards the cell body.
The axon carries impulses away from the cell body.
The myelin sheath, covering and protecting the axon, speeds up electrical transmission of the impulse.
The nodes of Ranvier, gaps which segment the myelin sheath, speed up transmission of the impulse by forcing it to jump across the gaps along the axon.
At the end of the axon are terminal buttons that communicate with the next neuron in the chain across the synapse (a gap).
In a neuron's resting state, the inside of the cell is negatively charged,
When a stimulus activates the neuron, the inside of the cell becomes briefly positively charged,
This causes action potential,
Creating an electrical impulse that travels down the axon towards the end of the neuron.
Synaptic Transmission - Chemical Transmission
A synapse separates each neuron within neuron networks (groups that use neurons to communicate with one another). The synapse is the space between the neurons, the presynaptic terminal, and the postsynaptic receptor site.
Signal within the neurons are transmitted electrically, but signals between the neurons are transmitted chemically (by synaptic transmission).
When an electrical impulse reaches the presynaptic terminal (the end of the neuron), it triggers the release of neurotransmitters from tiny sacs known as synaptic vesicles.
Neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain.
Once it has crossed the gap, it is taken up by the postsynaptic receptor sites (the dendrites of the next neuron).
The chemical message is converted back into an electrical impulse.