The Nervous System Flashcards
(67 cards)
1
Q
The nervous system is Divided into two parts
A
- Central nervous system-Main unit and connected to the rest of the body
- Peripheral nervous system-Carries information to and instructions from the brain
2
Q
- Nervous tissue is composed of
A
- Nerve cells – neurons
- Contain fibres which transmit nerve impulses
- Neuroglia– connective tissue
which supports neurons - Only found in the nervous system
- Does not transmit nerve impulses
3
Q
what are Neurons
A
- Basic units of the nervous system
- Long and narrow cells– up to 1m
- Easily damaged by toxins and lack of oxygen
- Not usually replaced when they die
- Some may have the ability to regenerate
4
Q
Neurons composed of
A
- Cell body
- Centre of the neuron. Contains the nucleus, cytoplasm and organelles e.g. mitochondria
- Dendrites
- Nerve fibres. Transmit nerve impulses TO the cell body
- Most neurons have several dendrites
- Axon
- A long single nerve fibre
- Transmits nerve impulses AWAY from the cell body
- Neurons generally have one axon
5
Q
what is * Myelin sheath
A
- Made of a white, fatty substance which covers the axon
- Protects it from pressure and helps speed up nerve conduction
6
Q
what is * Neurilemma
A
- A fine delicate membrane which surrounds the myelin sheath and helps regenerate nerve cells
- Composed of the cytoplasm and the nuclei of the Schwann cells which lie outside the myelin sheath
- Only found in the peripheral nervous system
7
Q
what are Nodes of Ranvier
A
- Gaps in the myelin sheath along the nerve
- Speed up the passage of nerve impulses along the fibre
8
Q
what are * Synapse
A
- A point where one neuron meets another
- Chemical messenger fills the gap and enables the impulse to be transmitted
9
Q
- End feet/axon terminals
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- Ends of the fibrils that make the axon more expanded
- Pass on the impulse from the axon to the dendrites of the next neuron
10
Q
Types of neurons – by function
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- Sensory neuron – afferent neurons
- Transmit impulses to the CNS so it can be processed
- Motor neuron – efferent neurons
- Transmit impulses to muscles, organs and glands
- Interneuron – found only in the CNS
- Connect one neuron to another
11
Q
Types of neurons – by structure
A
12
Q
basic Function of Neurons
A
- Receive signals (or information).
- Integrate incoming signals (to determine whether or
not the information should be passed along). - Communicate signals to target cells (other neurons or
muscles or glands).
13
Q
all Nerves and nervous tissue
A
14
Q
The nerve impulse – action potential
A
- Nerve cells transmit and receive nerve impulses throughout the body
- Impulses are created in response to internal or external stimuli
- Temperature, pressure, chemicals
15
Q
Resting membrane potential
A
- Positively charged sodium and potassium ions are present inside and outside the cell
- In a resting axon
- The concentration of sodium ions is lower inside the cell
- The concentration of potassium ions is higher inside the cell
- Due to
- Sodium potassium pump
- Many leakage channels for potassium
- Few leakage channels for sodium
- Result
- Inside of cell is more negative than the outside
- Chemical gradients for Na+ and K+ are created
16
Q
Sensory receptors – AP generation
A
- Stimuli are detected by sensory receptors
- The axon becomes temporarily more permeable to sodium ions which rush in
- The inside of the cell becomes more positive – depolarisation
- This reaches a threshold and then it starts becoming more negative – repolarisation
17
Q
Voltage gated channels
A
- Along the axon, there are voltage gated channels for both sodium and potassium
- These open when a threshold voltage is reached
- As they open, ions passively flow along the chemical gradient until a threshold to close is reached
- Voltage channels close and become inactivated
- The will not open for some time – refractory period
18
Q
Steps of an action potential
A
- Start = RMP = -70mv
- Disturbance causes threshold voltage for Na+ voltage gated channels to open - -55mv
- Na+ voltage gated channels open
- Na+ rushes in – rapid depolarisation till +30mv
- Na+ channels close, K+ channels fully open
- K+ rushes out – repolarisation
- Overshoot – K+ continues to rush out beyond RMP since they close very slowly – hyperpolarisation –85mv
- K+ channels close
- Na+/K+ pump restores RMP and returns ions to their original positions
19
Q
Refractory periods
A
- Why does an action potential proceed only one way?
- The answer lies in the refractory period
20
Q
action potential In the case of myelinated axons
A
- The action potential is generated only at the nodes of Ranvier
- Saltatory conduction
21
Q
Synapses
A
- Nerve impulses travel in one direction
- The impulse crosses the synapse from the axon terminal of the first neuron to the dendrites of the next neuron
- In between neurons, a neurotransmitter carries the message across the synapse
22
Q
Divisions of the
nervous system
A
23
Q
The central nervous system
A
- The brain
- Fills the cranium
- Stops developing in the 15th year of life
- Main mass exercising control over the body
- Three section
- Cerebrum
- Cerebellum
- Brain stem
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Q
The cerebrum - structure
A
- The largest part of the brain
- Divided into two cerebral hemispheres – left & right
- The outer layer is made of folds of grey matter
- Folds increase surface area
- There is white matter inside the grey matter
- White matter is composed of fibres which connect different parts
of the brain together
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The cerebrum - functions
* Controlling voluntary movement
* Interpreting and perceiving
conscious sensations like pain, heat and cold
* Controlling mental activity eg memory, intelligence and reasoning
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The cerebellum -structure
* Also known as the small brain
* Positioned in the posterior cranial fossa behind the pons Varolii, below the cerebrum and over the medulla oblongata
* Consists of two hemispheres, grey matter on the surface, white matter underneath
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The cerebellum - functions
* Co-ordinating muscular activity
* Subconsciously controlling and maintaining muscle tone and posture
* Maintaining balance and equilibrium of the body
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Hypothalamus - structure
* Situated deep within the cerebrum at the top of the brainstem with the pituitary attached to its base
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Hypothalamus - functions
* Helps with the regulation of body temperature, water balance and metabolism
* Centre for drives and emotions e.g. thirst, apetite, sex, pain and pleasure
* Regulates the pituitary gland forming the main link between the nervous and endocrine systems
* Secretes oxytocin and antidiuretic hormone/vasopressin (ADH) which are stored in the pituitary
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The brain stem Consists of three parts
* Midbrain
* Pons Varolii
* Medulla oblongata
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Midbrain
* Lies between the cerebrum and cerebellum and above the pons Varolii
* About 2cm long
* Consists of nerve cells and fibres
* Acts as a relay station of the brain
* Transmits messages to and from the spinal chord, cerebrum and cerebellum
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Pons Varolii
* Situated in front of the cerebellum, below the
midbrain and above the medulla oblongata
* Consists of nerve fibres which bridge the gap between the two hemispheres of the cerebellum
* Transmits messages to and from the spinal cord and cerebrum
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Medulla oblongata – structure
* Lowest part of the brainstem
* Located above the spinal chord and below the pons Varolii
* Construction is different from the cerebrum and cerebellum
* Has white matter on the surface and grey matter in the centre
* Known as a vital centre
* Controls the actions of the heart and lungs
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Medulla oblongata - functions
* Cardiac centre
* Controls the rate and strength of heart contraction
* Respiratory centre
* Controls the rate and depth of breathing
* Vasomotor centre
* Controls vasoconstriction and vasodilation
* Reflex centre
* Responds to irritants
* Controls vomiting, coughing, sneezing and swallowing
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The spinal chord - structure
* Extends from the medulla oblongata through the spinal vertebrae ending at the first lumbar vertebra
* Consists of white matter on the surface and grey matter inside
* Branches off into 31 pairs of spinal nerves ant part of 1 cranial nerve
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The spinal cord - functions
* Carries motor and sensory nerve fibres along its length
* Sends messages to and from the body and brain
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The meninges
* Membranes which protect the whole of the central nervous system.
* Three layers
* Dura mater
* Arachnoid mater
* Pia mater
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Dura mater (outer membrane)
* A double layer of tough, fibrous membrane
* It is thick and inextensible
* Periosteal layer
* Outer layer forms the periosteum of the skull
* Meningeal layer
* Inner layer (first protective covering of the brain) continues as the spinal dura mater as far down as the sacrum
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Arachnoid mater
* A delicate membrane
* Located under the dura mater and above
the pia mater
* Merges with the dura mater and covers the spinal chord as far as the sacrum
* Connects to the sub-arachnoid space found between the arachnoid mater and the pia mater
* Sub-arachnoid space
* Cushions the brain
* Filled with cerebrospinal fluid
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Pia mater
* Thin vascular membrane
* Tightly adhered to the surface of the brain and spinal chord
* Follows the contours of the brain (gyri and fissures)
* Continues along the length of the spinal chord
* Highly vascularised. Supplies blood to the brain and spinal chord
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Ventricles
* Four cavities inside the brain
* Two lateral ventricles. One on each side of the cerebral cortex
* The lateral ventricles are continuous with the 3rd ventricle
* The 3rd ventricle is continuous with
the 4th ventricle which runs along the brainstem
* Contain cerebrospinal fluid
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Cerebrospinal fluid
* Cerebrospinal fluid is produced by the lining of the ventricles
* Within choroid plexuses
* It is clear and colourless
* Resembles blood plasma in composition
* Contains protein, glucose salts and other substances
* Secreted into the ventricles and circulates around the whole brain and spinal chord
* Reabsorbed into the venous sinuses of the body through the arachnoid mater
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Cerebrospinal fluid - functions
* Protects the brain and spinal chord
* Forms a cushion between the bony cavities and nerves acting as a shock absorber
* Keeps the pressure around the brain and spinal chord constant
* Being immersed in CSF the net weight of the brain is reduced to 26g.
* This prevents excessive pressure on the base of the brain
* Chemical stability. CSF creates an environment to allow for proper functioning of the brain
* Transports nutrients and removes wastes and toxic substances
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Peripheral nervous system
* Concerns all the nervous system outside the central nervous system
* Contains motor and sensory nerves which transmit to and from the body to the CNS
* Consists of 12 pairs pf cranial nerves and 31 pairs of spinal nerves
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Cranial nerves
* 12 paired nerves which arise directly from the brain
* The first 2 (I-II) nerves (olfactory and optic) arise from the cerebrum
* Rest emerge from the brain stem
* Names relate to their function
* Numerically identified in roman numerals (I-XII)
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Trigeminal (V)
Opthalmic
* Sensory nerves supplying the lachrymal glands, conjunctive of the eyes, eyelids, forehead, anterior part of the scalp and mucuous membranes of the nose
Maxillary
* Sensory nerves supplying the lower eyelids, upper gums, upper teeth and cheeks
Mandibular
* Sensory and motor nerves
* Supply the teeth and gums of the lower jaw, ear and tongue. Motor supplying the muscles of mastication
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Facial (VII)
* Motor supply the muscles of the facial expression
* Sensory supply nerves of taste from the anterior part of the tongue
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Accessory (XI)
* Two parts
* Cranial – branches joining the vagus nerve to supply the pharynx and larynx
* Spinal – branches supplying the trapezius and sternocleido mastoidi
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Spinal nerves
* Begin in the spinal chord
* Supply all parts of the body not covered by the cranial nerves
* All are mixed nerves
* Divided into 31 pairs
* Cervical – 8 pairs
* Thoracic – 12 pairs
* Lumbar – 5 pairs
* Sacral – 5 pairs
* Coccygeal – 1 pair
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Spinal nerves2
* Cervical and thoracic nerves are named after the vertebrae at the level they exit the spinal chord
* Lumbar, sacral and coccygeal nerves leave the spinal chord at the level of the first lumbar vertebra and extend downwards inside the vertebral canal
* Exit the canal at different levels depending on their destination
* All spinal nerves except T2 to T12 branch out and regroup to form plexuses which supply different parts of the body
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Other structures
Cervical plexus
* Contains the 1st four cervical nerves
* Supplies the muscles of the neck, shoulder and skin
* Includes the phrenic nerve
Brachial plexus
* Includes the lower four cervical nerves and the 1st thoracic nerve
* Branches out to supply the muscles from the base of the neck to the fingertips and skin Thoracic (intercostal nerves)
* Supply the chest muscles and the main part of the abdominal wall Lumbar plexus
* Includes the 1st three lumbar nerves and part of the fourth
* Supplies the skin and muscles of the lower abdomen, thighs and groin Sacral plexus
* Includes the 4th and 5th lumbar nerves and 1st 4 sacral nerves
* Supplies muscles and skin of the pelvic area
* Main nerve is the sciatic nerve
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Function organisation of the PNS
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Somatic nervous system
* Conducts impulses from the CNS to skeletal muscle fibres
* The voluntary branch of the PNS
* Allows conscious control over the contraction of skeletal muscles
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Autonomic nervous system
* Conducts impulses from the CNS to cardiac and smooth muscles and glands
* An involuntary system controlled by the hypothalamus
* Nerves arise from the medulla oblongata
* Divided into the sympathetic and parasympathetic
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Sympathetic
* Nerves that arise from the spinal chord at the thoracic and lumbar region – thoracolumbar
* Forms ganglia just outside the CNS
* Nerves then extend to the organ or tissue they supply
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Sympathetic - functions
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Parasympathetic
* Consist of nerves that arise from the brain and sacral region of the spinal chord - craniosacral
* Form ganglia near to or inside the organ or tissue they supply
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Parasympathetic - functions
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Sympathetic/Parasympathetic graph
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what is Reflexes
* A reflex is an automatic movement produced by a sensory stimulus
* It is instant and involuntary
* Components
↓A sense organ – detects the stimulus
↓A sensory nerve travelling from the sensory organ
↓The spinal chord
↓A motor nerve starting from the spinal chord to the motor organ
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Reflexes
* Mostly protective
* Designed to stimulate the quickest motor responses possible
* Automatic reflexes
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sciatica
* Pressure on the roots of the sciatic nerve which becomes inflamed
* Causes pain down the back and outside of the thigh, leg and foot
* Treatment includes. mostly non surgical options and physical therapy
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Meningitis
* An infectious disease characterised by inflammation of the meninges
* Usually caused by a bacterial infection
* Symptoms include headache, stiff neck, fever & nausea
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Stroke
* A sudden loss of consciousness
* Due to rupture or occlusion of a blood vessel leads to a lack of oxygen in the brain
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Spina bifida
* A developmental birth defect involving the neural tubes
* A vertebra is malformed and the backbone does not form properly
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Concussion
* A mild traumatic brain injury after an impact
* Violently shaking the head and upper body can also cause concussions
* Results in an altered mental state that may include becoming unconscious
* Effects are usually temporary but can include headaches, problems with concentration, memory balance and coordination
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Shaken baby syndrome
* Occurs when the baby is shaken violently
* Babies have very weak neck muscles that cannot fully support their head
* Severe shaking causes the baby’s head to move violently back and forth
* May result in serious and sometimes fatal brain injury
