Lecture 15 - Cells and organisation of the nervous system Flashcards
Integrating and coordinating …meaning for our nervous system?
The nervous system senses the environment and then produces the appropriate response. It matches the sensory environment with our bodies needs
Maintaining homeostasis - integration, coordination and response
Integration often happens with you knowing it for example am I hungry? Do I want that kind of food?
Coordination e.g. preparation for eating, craving another type of food
Response e.g. order some food, go for Indian instead or walk away
Central nervous system
Central Nervous System (CNS) consist of the brain and spinal cord and is made out of neurons and glia
2 general cell classes that make up the CNS
Neurons
Glia
2 general cell classes that make up the PNS
Neurons
Glia
Peripheral nervous system (including the ENS)
Peripheral Nervous System (PNS) consists of the peripheral nerves (that come out of the brain and the spinal cord) and are made out of neurons and glia
CNS
Central nervous system
PNS
Peripheral nervous system
Neurons
The basic nerve cell of the nervous system containing a nucleus within a cell body and extending one or more processes. Nerve cells conduct information along the lengths of these processes.
Different shapes and sizes because they have different functions
These cells are specialised for transmission of information and there are 4 morphological types
Glia
Glia are non-neuronal cells in the CNS and PNS that do not produce electrical impulses. They maintain homeostasis, form myelin, and provide support and protection for neurons.
These are the support cells for neurons
There are 5 basic types - 4 in the CNS and 1 in the PNS. Each type has a special function
Structural components of a neuron
Dendrites - receive input and send info to the cell body
Cell body - contains nucleus and organelles and sums input (collects the input from the dendrites)
Axon (long structure that extends from the cell body) - carries electrical impulses (it carries information by transfusing electrical impulses) and may or may not be myelinated
Axon terminal(s) - Ends of the axon and this is where neurotransmitter release occurs (this is the last point where the signal goes)
In the CNS a group of cell bodies is called
Nucleus (plural is nuclei)
In the CNS a bundle of axons is called
Tract
In the CNS a group of cell bodies in the cerebral cortex or spinal cord is called
grey matter
In the CNS a bundle of axons in the cerebral cortex or spinal cord is called
White matter
In the PNS a group of cell bodies is called
Ganglion (plural is ganglia)
In the PNS a bundle of axons is called
Nerve
Functional components of a neuron
Input zone - composed of the dendrites and the cell body. Receives chemical signals from other neurons (receives neurotransmitters being released by other neurons)
Summation zone - axon hillock. Decision to transmit signal further is made here
Conduction zone - Signal is tranmitted along the axon, may be quite long, if the decision is made at the axon hillock that the signal should be transmitted further. Carry electrical signals between brain areas, to and from spinal cord, or to and from peripheral sensory receptors (an axon’s job is to conduct an electrical signal down its length)
Output zone - axon terminals. Contact with input zone of other neurons (can connect with other neurons or effector cells). Release of neurotransmitter = chemical signal
Axon hillock
The axon hillock is a specialised part of the cell body of a neuron that connects to the axon. It is here where the decision is made about whether to pass on the information
The axon hillock is where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon.
What is a process?
Refers to any projection from the cell body of a neuron
Multipolar neuron
Multiple processes emanate from the cell body (has an obvious axon and the rest of the processes are dendrites)
Bipolar neuron
Two processes emanate from the cell body (one dendrite and one axon)
Unipolar neuron
One process emanates from the cells body, then branches into dendrite and axon
Anaxonic neuron
No distinct axon, all process look alike
4 morphological types of neurons
Multipolar, bipolar, unipolar and anaxonic neurons
CNS glia cell names
Astrocytes, microglia, ependymal cells and oligodendrocytes
Astrocytes
Starshaped cell and they are the most abundant glial cells in the brain
Supply nutrients to neurons
Ensheath blood capillaries
Transmit information
Microglia
Immune cells of the CNS
Engulf microorganisms and debris
Ependymal cells
Line fluid filled space of the brain and spinal cord Have cilia (hair like processes) to circulated cerebrospinal fluid (the cilia wave which causes the CSF to circulate in a particular direction)
Oligodendrocytes
Support nerve fibres
Ensheath them with myelin (myelinates the axons)
PNS glia
Schwann cells
Support peripheral nerve fibres
Ensheath them with myelin (axon of the neuron is wrapped in Schwann cells which wrap their plasma membranes around the axon)
Similar to oligodendrocytes in the CNS
Myelin sheath
Fatty covering/ Lipid (fat wrapped around an axon
CNS comes from oligodendrocytes and in the PNS comes from Schwann cells
The myelin sheath increases conduction velocity (increases the velocity of the conduction of n electrical signal down an axon)
Where does the myelin sheath come from in the CNS?
oligodendrocytes
Where does the myelin sheath come from in the PNS?
Schwann cells
Nodes of ranvier
These are gaps between myelin
Increase conduction
Synapse
Communication between neurons occurs through a junction called a synapse
Junction between the cell sending the signal (axon terminal) and the cell that is receiving the signal (dendrites)
Chemical signal occurs in the synapse to bridge the gap between electrical signals
Simplified synapse process of transmitting a nerve impulse
Steps involved….
Nerve impulse depolarises terminal
Voltage gated Ca2+ channels open
Ca2+ influx causes vesicles to bind to the membrane and release neurotransmitter across the synaptic cleft
Neurotransmitter binds to the post synaptic receptors which open and depolarisation occurs
Nerve impulse is transmitted
How does the presynaptic neuron communicate with the post-synaptic neuron ?
The presynaptic neuron is before the synapse and is the neuron that is passing on the information. It contains synaptic vesicles, which are little packets that contain vesicles). This neuron releases neurotransmitters (chemical signal) from the axon terminal
These neurotransmitters go across the synaptic cleft and to the post-synaptic neuron.
The post-synaptic neuron is after the synapse and it is the neuron that is receiving the signal. This neuron contains receptors for the neurotransmitters
Afferent
Information that does into the brain
Sometimes known as ascending
e.g. sensing something in the environment
Efferent
Response that comes out of the brain
Sometimes known as descending
E.g. responding with an appropriate action
