8: The Nervous System Flashcards
What are the two roles of the human nervous system?
The human nervous system has two roles:
- To carry information quickly from one place to another
- To listen, analyse and act on the information
Describe the actions of the human nervous system:
The human nervous system acts very quickly, with short duration and very specifically targets using neurotransmitters
Describe the structure of the human nervous system:
The different parts of the human nervous system is made up of individual neurones. The neurones are physiologically identical in action, but vary based on their shape and the kind of information they carry
Millions of neurones run to all parts of the body and are organised into nerve bundles called nerves to keep things tidy
Nerve bundles are easier to wrap in protective tissues rather than wrapping each neurone individually
What are the divisions of the human nervous system?
The human nervous system is split into the central nervous system and the peripheral nervous system
What makes up the central nervous system?
The central nervous system is made up of the brain and the spinal cord
What is the role of the central nervous system?
The central nervous system receives and analyses information and sends commands to make things happen in other areas of the body
It is the analytical component for the whole body and often referred to as the control centre
What makes up the peripheral nervous system?
The peripheral nervous system is made up of all of the nerves outside of the central nervous system that carry information to and from the CNS and the tissues
What are the divisions of the peripheral nervous system?
The peripheral nervous system can be divided into two sections based on the type of information that is carried:
- The sensory division
- The motor division
What is the sensory division?
The sensory division is a division of the peripheral nervous system
The sensory division’s nerves carry signals to the CNS from sensory receptors located throughout the body which detect changes in the internal and external environment
What is the motor division?
The motor division is a division of the peripheral nervous system
The moto division’s neves carry signals from the CNS to muscles and glands to make changes
The motor division can be further sub-divided into two, based on the kind of actions that result from their signals
What are the divisions of the motor division?
The motor division can be sub-divided into the somatic motor branch and the autonomic motor branch
What is the somatic motor branch?
The somatic motor branch is a division of the motor division of the peripheral nervous system
What is the role of the somatic motor branch?
The somatic motor branch nerves carry signals to skeletal muscles that make them contract with conscious control
What is the autonomic branch?
The autonomic branch is a division of the motor division of the peripheral nervous system
What is the role of the autonomic branch?
The autonomic branch’s nerves carry signals to smooth muscle, cardiac muscles and glands, to make them work with no conscious control
What are the subdivisions of the autonomic branch?
The autonomic branch can be sub-divided into two divisions:
- The sympathetic division
- The parasympathetic division
What is the sympathetic division?
The sympathetic division is a sub-division of the autonomic division of the motor division of the peripheral nervous system
What is the role of the sympathetic sub-division
The sympathetic sub-division sends signals that cause the fight or flight responses in body organs and systems
Eg increased heart rate and dilated pupils
What is the parasympathetic sub-division?
The parasympathetic sub-division is a division of the autonomic branch of the motor division of the peripheral nervous system
What is the role of the parasympathetic sub-division?
The parasympathetic sub-division acts to restore the body to resting state and activity levels to normal after a sympathetic effect. Our lives are a balance between both effeccts
What are the main peripheral nerves of the bod?
The main peripheral nerves of the human body are:
- Cervical nerves
- Thoracic nerves
- Lumbar nerves
- Sacral nerves
- Coccygeal nerves
What are the main peripheral nerves of the head?
The main peripheral nerves of the ahead are:
- The filaments of the olfactory nerve
- Optic nerve
- Oculomotor nerve
- Trochlear nerve
- Trigeminal nerve
- Abducens nerve
- Facial nerve
- Vestibuocochlear nerve
- Glossopharyngeal nerve
- Vagus nerve
- Accessory nerve
- Hypoglossal nerve
What is a dermatone?
Each spinal/cranial nerve supplies a particular piece/ slice of the body,referred to as a derrmatone
Describe the anatomy of nervous tissue:
The nervous tissue is highly complex in structure and function. There are two types of cells in the nervous system, these are neuroglia and neurons
What are the two types of cells in the nervous system?
The two cells of the nervous system are:
- Neuroglia
- Neurons
What is the role of neuroglia?
Neuroglia are supporting cells. They protect and support neurons, by segregating and insulating them, as well as secreting a chemical to guide the young neurons to their proper connections
Neuroglia promote neuron health and growth
There are six types of neuroglia
What are the six types of neuroglia?
There are six types of neuroglia. Four of which are only found in the central nervous system, the other two are only found in the peripheral nervous system
What are the neuroglia of the peripheral nervous system?
There are two nerves in the peripheral nervous system:
- Satellite cells
- Schwann cells
What are the neuroglia of the central nervous system?
There are four neuroglia in the central nervous system:
- Astrocytes
- Microglia
- Ependymal
- Oliogodendrocytes
What is the role of satellite cells?
Satellite cells are found in the PNS
Satellite cells surround neuron cell bodies. Their precise role is unknown
What is the role of Schwann cells?
Schwann cells are found in the PNS
They surround nerve fibres to form the myelin sheath
What is the role of astrocytes?
Astrocytes are found in the central nervous system. They are the most commonly occurring neuroglia
They attach to neurons and their endings, cove capillaries in the brain and provide support to neurons. They regulate the chemical environment around neurons by controlling exchange between neurons and capillaries
What is the role of microglia?
Microglia are found in the CNS. They are small cells that monitor the health of neurons and carry out a defence role within the CNS, which immune cells cannot normally enter
What is the role of ependymal?
Ependymal are found in the CNS. They arre epithelial like cells found within the central cavities of the brain and spinal cord that produce and circulate cerebrospinal fluid
What is the role of oligodendrocytes?
Oligodendrocytes are found in the CNS and wrap around neurone fibres, forming myelin sheaths
What are neurons?
Neurones are also called nerves. Each individual neuron is a single cell specifically adapted to carry signals. They are complex cells that do not divide and so have to function for the organism’s lifetime. Each nerve cell has a cell body, axons, synaptic buttons and dendrites
What is a cell body in a nerve?
The cell body of a nerve is where the nucleus and all the usual organelles are found
What are dendrites in a nerve?
Dendrites are short tapering branching extensions of the cell which typically act as the receptive part of the cell
What are axons in nerves?
Axons are long narrow tubes that extend out from the cell and carry the nerve signal from A to B
What are synaptic buttons in nerves?
Synaptic buttons are swelling at the end of the axon that contain a chemical called a neurotransmitter which is released when the signal arrives. The neurotransmitter acts on the target cell to switch it on or off
How can neurons be classified?
Neurons can be classified on the basis of their structure and function. The functional description is either sensory neurons, interneurons or motor neurons
What is the role of nerve cells?
The role of nerve cells is to carry messages from one place to another. This applies even in the brain where signals can be incredibly complex, giving us the ability to carry out things like thought and imagination
What is action potential?
Action potential is the way in which nerve signals pass along the axon, like a wave of change
Describe the cell membrane:
Cell membranes are lipid bilayers which control which solutes can cross the membrane
What is the role of the cell membrane?
The cell membrane controls which solutes (molecules and ions) can cross the cell membrane. Generally only small and hydrophobic molecules can diffuse across the membrane. In nerve and muscle cells, there is a significant difference in the concentration of ions inside and outside
Describe ion movement in nerve cells:
There is a significant difference in the concentration of ions between the inside and outside of cells. This means that ion movement must be taking place across the cell membrane. If there is a concentration difference for an ion across a membrane, there will be a charge difference too, called a voltage
What are carrier/channel proteins?
Carrier/ channel proteins are the special group of membrane proteins that are routes for charged solutes to cross the membrane via
What causes a difference in ion potentials in and out of cells?
Ion concentrations inside and outside of any cell are different as a result of active and passive transport of ions through carriers and channels
What are membrane potentials?
Membrane potentials are the voltage difference across the cell membrane. They are present in all cells
What is the voltage of a membrane potential?
Membrane potentials are present in all cells and are typically between -30V and -70V, where the cell interior is negative in respect to the outside
What effect do membrane potentials have?
Membrane potentials can affect how ions move. The membrane potential is incredibly important in nerve and muscle cells, because the nerve signal is a charge to the membrane potential, and why nerve and muscle cells are excitable
Describe the movement of ions in cells:
Because opposites attract and likes repel, if the inside of the cell is positive and the outside is negative, then positive ions will want to enter and negative ions will want to leave
If holes are opened in the membrane that allow ions to cross, ions will move across the membrane down the concentration gradient, and along voltages
What is equilibrium potential?
Every ion that moves down the concentration gradient is taking a positive charge from inside. Ion movement will continue along its concentration gradient until the membrane potential reaches a value such that electrical attraction holds back the ion and equilibrium is reached. This means the ion doesn’t move anymore. This is called the equilibrium potential
What is voltage?
Voltage is the measure of potential energy generated by separated charges
In cells, this separation is done by the cell membrane
Describe the charges of a resting nerve:
In a resting nerve, the interior is more negative than the exterior
This is the resting membrane potential
What does the speed of conduction depend on?
The speed at which the signal passes along the nerve is dependent on two factors
- The diameter of the nerve fibre
- If the nerve is wrapped by glial cells (eg Schwann cells)
How does the diameter of the nerve fibre affect its speed of conduction?
A thicker axon conducts faster than a thin one
The higher the diameter of the nerve fibre, the higher the speed of conduction
How do glial cells affect the speed of conduction in a nerve?
If the nerve is wrapped in glial cells (eg Schwann cell) the nerves can carry signals much faster by saltatory conduction
What is saltatory conduction?
Saltatory conduction is where waves jump from node to node, which is much quicker than activating every segment. This happens when glial cells wrap the axon with multiple layers of myelin which prevents the movement of ions across the membrane, meaning ions can only cross at the nodes of Ranvier
What is myelin?
Myelin is a white fatty material, which when wrapped around the axon of a nerve, prevents the movement of ions across the membrane
What are the three parts of a synapse?
A synapse has three parts:
- Synaptic button
- Synaptic gap
- Post-synaptic membrane
What is the synaptic button?
The synaptic button is a swelling at the end of the axon. Inside the synaptic bulb are vesicles that contain a chemical called a neurotransmitter
What is a synaptic gap?
A synaptic gap is the space between the two cells
What is the post-synaptic membrane?
The post synaptic membrane is the membrane of the receiving target cell
What happens when an action potential arrives at the synaptic bulb?
When the action potential arrives at the synaptic bulb, a neurotransmitter is released into the synaptic gap. It diffuses across the gap to the target cell’s post-synaptic membrane on the target cells are receptors which open or close to allow particular ions to cross. This causes a change in the membrane potential in the receiving cell, leading to a change in its behaviour: eg contract, secrete etc
What is a receptor?
Receptors are special proteins found on the target cell membrane. They bind to the neurotransmitter and open or close channels, allowing particular ions to cross. This causes a change in the membrane potential of the receiving cell, and therefore a change to its behaviour
What are synapses?
Synapses are where the nerve meets its target cell
What is the role of a synapse?
The synapse is here the nerve meets its target cell. They provide a mechanism for cells to influence other cells and for messages to be altered
Synapses provide a target for pharmacological intervention eg drugs blocking and preventing neurotransmitters binding
What is the role of excitatory neurotransmitters?
Excitatory neurotransmitters switch on their target cell
If an excitatory neurotransmitter is released, there will be a depolarisation of the target cell, called an excitatory post synaptic potential
What is the role of inhibitory neurotransmitters?
Inhibitory neurotransmitters switch off their target cell
If an inhibitory neurotransmitter is released, the target cell will be hyper polarised, called an inhibitory post synaptic potential
What happens when an excitatory neurotransmitter is released?
If an excitatory neurotransmitter is released, there will be a depolarisation of the target cell, called an excitatory post synaptic potential
What happens when an inhibitory neurotransmitter is released?
If an inhibitory neurotransmitter is released, the target cell will be hyper polarised, called an inhibitory post synaptic potential
Give an example of an excitatory neurotransmitter:
Noradrenaline is an excitatory neuorotransmitter
Give an example of an inhibitory neurotransmitter:
GABA is an inhibitory neurotransmitter
What is the central nervous system made up of?
The central nervous system comprises of the brain and spinal cord
What is the role of the central nervous system?
The central nervous system is the integration and control centre for the body. It receives input from the PNS and delivers output to the PNS and tissues
What is afferent?
Afferent is the input received by the CNS from the PNS
What is efferent?
Efferent is output to the PNS from the CNS
How does the nervous system develop in an embryo?
The neural tube is one of the first structures that can be identified. From the neural tube, the whole of the nervous system will develop
Hat is the cerebral hemisphere?
The cerebral hemisphere is an area in the adult’s brain structure that is part of the CNS
Describe the development of the cerebral hemispheres:
The cerebral hemispheres develop from the telencephalon and form the bulk of the brain. They have three main components in both the left and right hemispheres
What are the three main components of the cerebral hemispheres?
The three main components of the cerebral hemispheres in the left and right hemisphere are:
- Cortex (aka grey matter)
- White matter
- Basal nuclei
What is the cortex?
The cortex is the grey matter found in the cerebral hemispheres. It is made up of billions of nerve cells
What is white matter?
White matter is made up of billions of myelinated nerve axons and found in the cerebral hemispheres
What are basal nuclei?
Basal nuclei are islands of grey matter that communicate with lots of other parts of the hemispheres. They are found in the cerebral hemispheres
What areas can the hemispheres be divided into based on convolutions?
The hemispheres can be divided into different areas based on their convolutions:
- Ridge- gyrus
- Valley- sulcus
- Large valley- fissure
What ways can the hemispheres be divided in?
The hemispheres can be divided into three based on convolutions, or into three based on function
What is the name of the model which shows functional activity of the brain?
The Brodmn model shows functional activity of the brain
What areas can the hemispheres be divided into based on function?
The hemispheres can be divided into three based on function:
- Motor
- Sensory
- Association
What is the role of white matter?
White matter carries signals to and from the grey matter to connect different areas. There are three types of fibres
What are the three types of fibres in white matter?
The three types of fibre in white matter are:
- Commissural fibres
- Association fibres
- Projection fibres
What are commissural fibres?
Commissural fibres connect the two hemispheres to the corpus collosum
It is the largest example
What are association fibres?
Association fibres connect the different areas of one hemisphere
What are projection fibres?
Projection fibres connect to lower brain centres and the spinal cord to send and receive information from the body
What is the role of the basal nuclei?
The basal nuclei have an important holistic role in receiving input from the entire cerebral cortex and input from structures further down the neural tube. The BG activity includes:
- Regulating cognition and attention
- Starting, stopping and monitoring the intensity of movements executed by the cortex
- Inhibiting une cesar y movements
- Enabling multi-tasking
What is the diencephalon comprised of?
The diencephalon is comprised of the thalamus, hypothalamus and epithalamus
What is the role of the thalamus?
The thalamus is the part of the diencephalon where sensory nerve signals from all parts of the body converge and synapse. It forms an important relay centre and sorts information before sending it to the relevant part of the cortex
What is the role of the epithalamus?
The epithalamus is the part of the diencephalon where the pineal gland extends out from its posterior surface and secretes the hormone melatonin to regulate the sleep/wake cycle and some aspects of mood. Part of the epithalamus makes the cerebrospinal fluid that surrounds the brain and spinal cord
What is the hypothalamus?
The hypothalamus forms the floor of the diencephalon. A stalk from the base of the hypothalamus ends in the pituitary gland
What is the role of the hypothalamus?
The hypothalamus is an important control centre vital to homeostasis. Its roles included:
- Autonomic control
- Emotional response
- Body temp regulation
- Food intake regulation
- Water balance regulation
- Sleep/wake cycle regulation
- Endocrine system control
What is another name for the brain stem?
The brain stem is sometimes called the primitive brain because it controls basic bodily functions
What are the component structures of the brain stem?
The component structures of the brain stem are:
- The midbrain
- The pons
- The medulla oblongata
Describe the structure of the midbrain:
The mid brain has:
- A fluid component called the cerebral aqueduct
- A layer of grey matter called periaqueductal grey surrounding the CA
- Four dome like protrusions called superior and inferior colliculi on the dorsal surface
- A pigmented area called the substania nigra
What are the roles of the midbrain?
Different components of the midbrain have different roles:
- Perriaquedductal grey- important role in suppression
- Superior and inferior colliculi- co-ordinate head and eye movements
- Substantia nigra- provides input of dopamine to the basal ganglia, important in fine muscle control
What are the components of the pons?
The pons contain a specialist area called the pneumotaxic centre and some cranial nerves have their origin here
What are the roles of the pons?
Within the pons, the pneumotaxic centre controls breathing rhythm
What are the components of the medulla oblongata?
The remaining cranial nerves that don’t originate in the pons do so here. The medulla oblongata also contains autonomic reflex centres for the cardiovascular and respiratory centres
What are the roles of the medulla oblongata?
Motor nerves cross in the medulla oblongata, called decussating. This means the left cortex looks after the right side of the body and vice versa. The medulla oblongata also contains autonomic reflex centres for the cardiovascular and respiratory systems
What is the role of the cardiovascular centre in the medulla oblongata?
The cardiac centre adjusts the force and rate of heart contraction
The vasomotor centre changes blood vessel diameter to regulate blood pressure
What is the role of the respiratory centre in the medulla oblongata?
The respiratory centre controls the rate and depth of breathing and with the centre in the pons, controls respiratory rhythm
What is the role of the cerebellum?
The cerebellum connects with the pons and medulla. It processes inputs room te cerebral motor cortex, various brain stem nuclei and sensory receptors in muscles and tendons
The activity in the cerebellum is unconscious but provides the rest of the brain with a body awareness map because of the body image we have created in the cerebellum, which allows us to point to certain areas of our body correctly with our eyes shut
What are two of the functional descriptions of brain activity?
Two functional descriptions of brain activity that involve a number of brain areas are:
- The limbic system
- The reticular formation
Describe the limbic system:
The limbic system is a functional description of brain activity, which involves a number of brain areas
It is formed from parts of the cerebral hemispheres and diencephalon
What is the role of the limbic system?
The limbic system’s components provide our emotional and affective brain
Describe the reticular formation:
The reticular formation is a functional description of brain activity that involves a number of brain areas
Its structures include the medulla oblongata the pons and the midbrain which together form the reticular activating system
What is the role of the reticular formation?
The reticular activating system of the reticular formation governs the arousal of the brain as a whole. This keeps the cortex alert and conscious
Severe injury ti this system from a twist in the brainstem can result in a coma
Describe the structure of the spinal cord:
The spinal cord has grey matter at its centre, surrounded by white matter. Within the grey matter are interneurones
Sensory nerves enter the grey matter from the dorsal side and motor nerves exit ventrally. Once the two nerves leave the spinal cord, they run together as mixed spinal nerves
What is a dermatome?
A dermatome is the area of the body served by a spinal nerve
What is the role of the spinal cord?
Information passing to and from the brain for the whole body passes along the spinal cord (except head/neck, which is dealt with by cranial nerves)
Information running to the brain uses ascending nerves, and from the brain uses descending nerves. Runs in columns within the cord
What are interneurones?
Interneurones are found within the grey matter of the spinal cord. They connect sensory and motor nerves, which forms the reflex arc and communicates to the brain
Describe the nerves in the autonomic nervous system:
The autonomic system has two branches:
- Parasympathetic- nerves exit the CNS as cranial or spinal nerves at the sacral level
- Sympathetic- nerves enter the spinal cord and exit at each level of the thoracolumbar spinal nerves
The autonomic nerve path from the CNS to the tissues is a two nerve path:
- Nerve 1: the ganglion between nerve one and two
- Nerve 2: the post-ganglionic neurone runs from synapses to the tissues
What are the twelve cranial nerves?
Twelve cranial nerves supply the structures of the head and neck:
* See cheat sheet for names and roles
What are the different types of cranial nerves?
The different types of cranial nerves are:
- Sensory
- Somatic motor
- Somatic motor and sensory
- Somatic motor and parasympathetic
- Somatic motor, sensory and parasympathetic
What is the role of sensory nerves?
Sensory nerves send inflation to the brain
What is the role of somatic motor nerves?
Somatic motor nerves carry information away from the brain
What is the role of somatic motor and sensory nerves?
Somatic motor and sensory nerves carry both somatic and sensory information
What is the role of somatic motor and parasympathetic nerves?
Somatic motor and parasympathetic carry motor and autonomic information
What is the role of somatic motor sensory and parasympathetic nerves?
Somatic motor sensory and parasympathetic nerves carry sensory motor and autonomic information
What are the meninges?
The meninges are three connective tissue membranes that surround the brain and protect the brain and spinal cord
What are the three types of meninges?
The meninges from the outer later to the inner layer are:
- The dura
- The arachnoid
- The pia
Describe the dura:
The dura is the outermost layer of the meninges, which protect the brain and spinal cord
It is a strong connective tissue later, with two layers fused together. Its outer layer is attached to the inner surface of the skull
Describe the arachnoid:
The arachnoid is the middle layer of the meninges, which protects the brain and spinal cord
The layer is a looser brain covering, separating the dura with a thin fluid space called the subdural space, filled with cerebrospinal fluid and containing large blood vessels that serve the brain
The arachnoid is fine and elastic, meaning the blood vessels are poorly protected
Projections from the arachnoid are called arachnoid villa
What is the role of arachnoid villi?
Arachnoid villi are found in the arachnoid, which is the middle layer of the meninges which protects the brain and spinal cord
Arachnoid villi project from the arachnoid and into the dura, to allow cerebrospinal fluid to be reabsorbed into the blood
Describe the pia:
The pia is the innermost laye of the meninges, which protect the brain and spinal cord
It is composed of delicate connective tissues and contains tiny blood vessels
It clings tightly to the brain, following its every convolution
Where is cerebrospinal fluid found?
Cerebrospinal fluid is found in and around the brain and spinal cord
What is the role of cerebrospinal fluid?
Cerebrospinal fluid acts like a cushion to give buoyancy to the CNS
What are ascending pathways used for?
Ascending pathways are used for sensory information
How are ascending pathways used?
Receptor cells detect a stimuli and transducer this into a nerve action potential signal which runs up ascending pathways to the brain, to inform of the stimulus
Signals from different receptor types travel to the brain via different pathways as they have different targets in the brain
Most sensor signals have a pathway made up of three neurones. The precise arrangement of the component nerves varies upon the type of information being carried
Where do conscious responses come from in the brain?
The cerebral cortex is targeted for a conscious response
Where do sub-conscious responses come from in the brain?
The cerebellum is targeted for a sub-conscious response
What are descending tracts used for?
Descending tracts are used to carry motor information
The pathways carry signals that are mainly concerned with control of movement, muscle tone, spinal reflexes and spinal autonomic function
How are descending tracts used?
Most of the motor pathways are made up of two nerves.
One runs from the source to the ventral grey matter of the cord, where the first synapse takes place
The second nerve runs from this grey matter space to the tissue
What does the corticospinal nerve connect?
The corticospinal nerve connects the cortex to the spinal nerves
What does the rubrospinal nerve connect?
The rubrospinal nerve connects the red nucleus of the mid-brain to spinal nerves
What does the tectospinal nerve connect?
The tectospinal nerve connects the superior colliculi of the mid-brain to cervical spinal nerves
What does the vestibulospinal nerve connect?
The vestibulospinal nerve connects the vestibular nuclei in the pons and medulla oblongata to the cervical and lumbar cord
What does the reticulospinal tract connect?
The reticulospinal tract connects reticular formations of the pons and medulla to spinal nerves
