- Created by: TomHurst74
- Created on: 19-02-19 12:21
Divisions of the nervous system
The nervous system includes the central nervous system (CNS) which consists of the brain and spinal cord. This is where all the complex processing of information is done and decisions are made.
The brain provides conscious awareness and is involved in all psychological processes, and is split into two hemispheres. The cerebral cortex is more developed in humans than animals.
The spinal cord transports messages to and from the peripheral nervous system, and it is responsible for reflexes.
The nervous system also includes the peripheral nervous system (PNS) which brings information from the senses to the central nervous system and transmits information from the central nervous system to the muscles and glands. This transmission is done via million of neurons. It is subdivided in two, the autonomic nervous system and the somatic nervous system.
The somatic nervous system controls voluntary movement. It receives information from the senses and transmits it to the central nervous system. It also transmits information from the central nervous system to the direct movement of muscles
The autonomic nervous system is responsible for vital functions such as heart rate. It transmits information to and from the internal body organs like the lungs. Therefore, the autonomic nervous system controls automatic and involuntary movements. This system is further divided into two sections:
Sympathetic nervous system: involved in fight or flight response
Parasympathetic nervous system: involved in fight or flight response
The organisation of the nervous system
Neurons are nerve cells that process and transmit messages through electrical and chemical signals.
Structure of neurons
The cell body contains the nucleus and has dendrites extending from it, which carry electrical signals from other neurons to the cell body. While the axon, an extension of the cell body, carries the signals away from the cell body. The axon, for motor and sensory neurons, is coated in a myelin sheath, as fatty substance which increases the speed at which the impulses propagate. There are breaks in the sheath called nodes of Ranvier which are between 0.2 and 2mm wide, these speed up transmission by forcing the signal to jump across the gaps.
Types of neurons
Sensory neurons have long dendrites and two short axons with myelin sheaths. They carry signals from receptors in the peripheral nervous system to the central nervous system.
Motor neurons have short dendrites and long axons with myelin sheaths. They carry signals from the central nervous system to effectors (muscles and glands).
Relay neurons have short dendrites and one very short axon without a myelin sheath. They connect the sensory and motor or other relay neurons, they are found in the brain and spinal cord.
Neurons transmit pulses of electrical activity known as action potentials.
Action potential: A short increase or decrease of electrical activity in the membrane of a neuron, transmitting a signal away from the cell body.
Electrical transmission: the firing of a neuron
When a neuron is in a resting state, the…