Chapter 4 - Central nervous system, peripheral nervous system & neurons: structure & function

Node of Ranvier

A gap between successive segments of the myelin sheath where the axon membrane is exposed.

Neurotransmitter

Chemicals that help the communication across nerve synapses, released by the axon terminal.

Communication between neurons

Information is transferred through the body via neurons. The information being passed through in the form of electrical impulses is received from the dendrites with the help of neurotransmitters, where it travels through the soma, down to the axon and to the axon termina, known as a presynaptic nerve, where neurotransmitters are released to help the impulses synapse to the next neuron's dendrites, known as a postsynaptic neuron. Where the process repeats itself.

Myelin

Myelin is a fatty substance that covers the axon to insulate it from the surrounding fluid and from other neurons. It is just the axon that is covered, not the cell body. Myelin is produced in the brain and spinal cord by glial cells. The process of producing myelin is called myelination, where neurons are faster in the speed of conduction -> the speed in which messages move through the nervous system

Neurons

Neurons receive information from other neurons, process this information, and then communicate it to other neurons.

The Central Nervous System (CNS)

One of the two major devisions of the nervous system. The CNS comprises of the brain and spinal cord. The spinal cord runs from the brain stem to the lower middle section of the spine. It enables the brain to communicate to the rest of the body by conveying messages from the brain to the PNS and from the PNS to the brain. The spinal cord is separated into segments with the upper segment responsible for communication between the brain and the upper parts of the body. The lower section is responsible for legs, toes, feet etc.

Reacting to our senses

Our ability to detect stimuli through the sensory neurons gives our brains an opportunity to consciously respond to hazards in our environment Reaction times, of both voluntary and involuntary responses, can be studied in psychology

Using our senses

Our brain and body are in continuous communication with each other. This communication can be either from our senses to the brain to be interpreted as they detect incoming information from our environment OR from our brain to our somatic nervous system (skeletal muscles) so that we respond to our environment. Sensory neurons play an important part in our lives by transmitting sensory information from our environment to our brain. Our ability to touch, taste, see, hear and smell all comes from a process beginning with our sensory neurons registering an external stimulus, and then relaying that information to the CNS. Motor neurons can then carry signals from the brain and back to the muscle fibres so that our bodies can respond to the stimulus.

Reflex actions

Reflexes are involuntary actions, in response to a stimulus, that do not involve the brain. They occur almost instantly when triggered by a certain external stimulus. A reflex arc allows us to react quickly to a stimulus. In higher-functioning animals, a reflex arc is a neural pathway in which the sensory neurons send information immediately to the motor neurons via a synapse in the spinal cord, known as a relay neuron. This ability to bypass the brain means reaction time in reflex actions is much quicker than if our brain had to process and respond to that stimulus.

SAME neurons

Sensory = carries information from the body and outside world to the CNS Afferent = carry messages from the body (CNS) to the brain to be processed Efferent = carry messages from the brain to the body (CNS) Motor = carries information from the CNS to the effector to carry out the actions

Autonomic Nervous System (ANS)

The autonomic nervous system: responsible for the communication of information between the CNS and the body's non-skeletal, internal organs and glands that carry out the basic bodily functions necessary for survival, such as digestion and heartbeat.

Parasympathetic Nervous System

The parasympathetic nervous system operates in circumstances where it is relatively calm. It is responsible for maintaining automatic day-to-day bodily functions such as digestion, normal heart rate, and normal breathing, the regular bodily functioning, homeostasis, or returning it to this state. Basically the sympathetic nervous system prepares the same organs to deal with threats or stressors, while the parasympathetic nervous system calms it down

Neural Pathways

The pathways that nerve impulses take along the neurons. They allow one part of the Nervous System to communicate with another.

Peripheral Nervous System (PNS)

The peripheral nervous system has two functions: - To communicate information from the body's organs, glands and muscles to the CNS, from not the outside world (such as environmental temperature and sensation on skin via sensory neurons) and the inside world (such as aches and pains) - To communicate information to the CNS to the body's organ, glands and muscles, bia motor neurons. The CNS has two subdivisions, the Somatic Nervous System and the Autonomic Nervous System, the ANS also has another two subdivisions, the Sympathetic Nervous System and the Parasymapthetic Nervous System.

Somatic Nervous System (SNS)

The somatic nervous system: responsible for the voluntary movement of skeletal muscles and motor neurons communicate messages from the CNS to the particular muscles that an organism intends to move at any particular moment with Sensory neurons

Sympathetic Nervous System

The sympathetic nervous system is like an emergency system that becomes active when the organism perceives itself to be in danger or in times of stress. It has a survival role because it readies the body for actions such as running away, fighting the threat, or remaining (freezing). This is known as the fight, flight or freeze response.

Synapses

Tiny spaces between neurons; the gaps between neurons are referred to as synaptic gaps. A synapse occurs when information jumps from one nueron to another

Glial cells (glia)

are not part of the neuron, but have an important role in supporting neurons. They are also known as neuroglia, or simply glia, which hold/ing neurons together. There are four identified functions of glial cells: 1. To surround neurons and hold them in place 2. To supply nourishment and oxygen to neurons 3. To remove dead neurons 4. To insulate one neuron from another and increase the speed of transmission of nerve impulses. To do this, glial cells produce myelin.

Axon

is a nerve fibre that carries information away from the soma to their ends toward other cells that communicate with the neuron. This information is referred to as 'action potential', which consists of brief changes in the electrical charge of the axon. The end of each axon has terminal buttons that secrete a chemical called a neurotransmitter whenever information is sent down the axon in the form of electrical impulses.

Soma

is the cell body. It is the largest part of the neuron and controls the metabolism and maintenance of the cell.

Dendrites

receive information from other neurons or sensory receptors via synapses and deliver this to the cell body or soma.