NERVOUS SYSTEM Flashcards
(46 cards)
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OVERVIEW OF THE NERVOUS SYSTEM
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CELLS AND TISSUES
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Nervous tissue: neurons and glial cells
PNS
- cranial and spinal nere
- sensory 9afferent) sends impulses to CNS
- mixed with both sensory and motor fibres
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NEURONES - CELL BODY
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CELL BODY: The body makes up the grey matter of the NS
- The body is at the periphery of the brain & spinal cord
- Receive, conduct and transmit information
- Gial cells are supported by neurons
- Gial cells, collectively known as neuroglial nerve tissues
- nerve cells & bund;es of axons together = nerves
- need a consistent supply of O2 and glucose
- generate & transmit electrical impulses = action poteintal
- Action potentials are initiated by stimuli from inside or outside the body
- outside the body, changed the concentration of co2 in blood changing breathing
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AXON AND DENDRITES
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- extension of cell bodies
- axons found inside the brain
- found in groups called tracts, the periphery of the spinal cord
- Each nerve cell has an axon that forms an axon hillock
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STRCUTRES OF AXON
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- cytoplasm surrounded by a membrane called the axolmma
Neurons are myelinated or unmyelinated - ## Myelinated neurons have a myelin sheath of Schwann cells
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DENDRITES
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- short process of receiving and carrying nerve impulses towards the body cells
- dendrites similar structure to axons, but are shorter and branch
- Dendrites make up part of the synapse in motor neurons
- receptors resposne to specific stimuli
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Q
SCHWANN CELLS
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- Example of glial cells
- wrapped around an axon covered by a number of plasma membranes
- plasma membrane, small amount of fatty substances = myelin
- outer layer: plasma membrane nerilemma
- the nodes of ranvier tiny areas of axolemma and nodes help radpid tranmission of action potential
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NERVES
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- made of many neurons in a bundle of nerve fibres
- protective connective tissues
> endoneurium: tissue surrounding each fibres
> perineurum: smooth connective tissue each bundle of fibres
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NERVES FIBRES AND NERVES
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- nerve made up of bundles of nerve fibres
- each fibre has a axon
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SENSORY NERVES
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- Carry info from the body to the spinal cord
- continue to the brain or connector neurons of reflex arcs in the spinal cord
- receptors found in skin, muscles, joints
-specialised ending of the sensory nerves - receptors respond to different stimuli inside and out of the body
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MOTOR NERVES
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- formed from the brain, spinal cord & autonomic ganglia
- transmit nerve impulses to effector organs: muscle and glands
2 types of motor nerves: - somatic nerve: voluntary and reflex skeletal muscle contractions
- autonomic nervous system: cardiac and smooth muscle contraction and glandular secretions
autonomic ganglia = clusters of neuronal cell bodies & dendrites
- junction between autonomic nervous system
- starting at the central nervous system & autonomic nerve innervating organs in periphery
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MIXED NERVES
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- in the spinal cord, sensory & motor nerves, arranged in separate groups
- outside the spinal cord, sensory & motor nerves are enclosed in the same connective tissue
- tissue sheath known as mixed nerve
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NEUROGLIA
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- GLIAL cells support the neurons of the CNS
- Glial cells continue to replicate throughout our lives (neurons cannot divide)
4 types of glial cells: astrocytes, oligodendrocytes, ependymal cells & microglia
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GLIAL - ASTROCYTES
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NEUROGLIA - ASTROCYTES
- found next to blood vessels
- form part of the blood-brain barrier
- blood blood-brain barrier protects the brain from toxic substances and chemical variations in the blood
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NEUROGLIA - OLIGODENDROCYTES
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- found in clusters around the nerve cell bodies in grey matter, found along the length of myelinated nerve fibres
- Myelin is a lipid-rich substance that insulates myelinated nerves = speeding up their impulses
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NEUROGLIA - EPENDYMAL CELLS
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- in line with cerebellar cavities (ventricles) & central canal
- produces & circulates cerebrospinal fluids (CSF) found in chambers
- structures with capillaries called the choroid plexus
- CSF = colourless liquid protects the brain and SC against chemical & physical injuries, carrying O2, glucose and other necessary chemicals from the blood to neurons and neuroglia
- Ependymal cells form the epithelial lining of the ventricles of the brain and the central canal of the spinal cord
- The cells that form the choroid plexus of the ventricles secrete CSF and those with cilia help the flow of CNS
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NEUROGLIA - MICROGLIA
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- migrate from monocytes that migrate from blood to the nervous system
- found throughout the brain
- microglia phagocytic = removal of microbes and damaged tissue
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ACTION POTENTIAL (NERVE IMPULSES)
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- happens when sensory nerve endings (dendrites) are stimulated by an impulse from another nerve
- Movement of ions across the nerve cell membrane = action potential
RESTING MEMBRANE POTENTIAL: electrical charge on each side of the nerve cell membrane
- charge on the outside of positive and inside is negative
- ions diffuse down their concentration gradient, K+ outwards and Na+ into cells
- stimualted = channels in the membrane open & Na floods into cells from ECF = depolarisation (cell’s membrane potential becomes less negative (more positive)), triggering action potential
- depolarisation = rapid enables conduction of nerve impulses along the entire length of neurons.
- the movement of Na and K returns the membrane potential to its resting state
- Soduim-potassium expels from Na and cells in exchange for K, returing to orignal resting state and repolorising the neruon
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SYNAPSE AND NEUROTRANMITTERS
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- No physical contact between neurons
- An action potential passes from presynaptic neurons to postsynaptic neurons through called synapse
- neurotransmitter synthesised by nerve cell bodies, transported along the axon and stored in synaptic vesicles
- released by exocytosis in response to an action potential and diffuses across the synaptic cleft
- The neurotransmitter acts on specific receptor sites and the postsynaptic membrane
- presynaptic neurons break into tiny branches terminate into small swellings = syanptic knobes/terminal buttons close to the dendrites & cell body of the postsynaptic neruon space between them in synaptic cleft
- neurotransimmer acted on postsynaptic membrane, inactivated by enzyme or taken back into the synaptic knob
- neurotransitters have excitatory effect on postsyantpic recpetors but can be inhibitory
- examples: dopamine, histamine, serotonin
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CENTRAL NERVOUS SYSTEM
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- brain and spinal cord
- brain protected from damage and injury by the skull ad the spinal cord protected by spianl colum = formed from vertebrae
- brain and spinal cord are protected by meninges = membranes
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MENINGES
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3 layers of tissue:
> dura mater (outer)
> arachnoid mater
> pia mater (inner)
- brain subdural space between dura mater and arachnoid mater containing a small amount of serous fluid.
- Subarachnoid space separates the arachnoid and pia maters contain cerebrospinal fluid (CSF)
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VENTRICLES OF THE BRAIN AND CEREBROSPINAL FLUID
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RIGHT & LATERAL VENTRICLES, 3RD AND 4TH VENTRICLES
- circulates from the ventricles through the subarachnoid space around the brain and spinal cord
-CSF = clear, alkaline fluid and specific gravity consists of water, mineral salt, glucose, plasma protein (albumin & globulin), leukocytes, a small amount of creatinine and urea
- secreted into ventricles = choroid = rich in blood vessels surrounded by ependymal cells in the lining of the ventricles’ walls
- CSF acts as a cushion/shock absorber between the brain & skull
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THE BRAIN
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- blood supply to the brain from the circulus arteriosus (circle of Willis)
- keep a constant supply of oxygen and glucose to the brain
- blood drains into dural venous sinuses and jugular veins
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CEREBRUM
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- the largest part of the brain
- divided into left and right cerebral hemispheres
- Each cerebral hemisphere is divided into lobes: frontal, parietal, temporal & occipital
- Deep inside the brain, the cerebral hemispheres are connected by a mass of white nerve matter = corpus callosum
- superfical part of the cerebrum composed of grey matter (nerve cell bodies) makes up cerebral cortext
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FUNCTION OF THE CEREBRAL CORTEX
MOTOR: directing muscle movement
SENSORY: receives and decodes sensory impulses
ASSOCIATION: integrating and processing complex mental function e.g intelligence, memory, reasoning, judgement and emotions
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DIENCEPHALON
- connects the cerebrum and the midbrain
- consists of the thalamus, hypothalmus, pineal gland and optic chiasm (where the optic nerve crosses)
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BRAIN STEM
contains: midbrain, pons & medulla oblongata
MIDBRAIN: nuclei & nerves fibres connect the cerebrum with the lower parts of the brain and the spinal cord. Nuclei relay stations for ascending and descending nerve fibres
- Nuclei have an important role in auditory and nerve reflexes
PONS: anterior to cerebullum
- consists of nerve fibres bridging between the higher levels of the brain and the spinal cord
- Pons processes information from cranial nerves
- sensory information from face, scalp, mouth, nose & motor control of chewing
- hearing and balance
- Pons contains pneumotaxic areas that work with the respiratory centre in the medulla oblongata to control respiration
MEDULLA OBLONGATA: continuous with the spinal cord below
- outer aspects of medulla, white matter and grey matter = more central
- cardiovascular centre, respiration centre & reflex centre of vomiting, coughing, sneezing and swallowing
- motor nerves descending from the motor area in the cerebellum to the spinal cord, crossing from one side to another
- The left hemisphere of the cerebrum controls the right half of the body
- the main pathway to the skeletal muscles
- happens in some sensory nerves crossing over is called decussation
RETICULAR FORMATION: collection of neurons in the core of the brain stem surrounded by numerous neural pathways conducting ascending and descending impulses between brain and the spinal cord
- synaptic links with parts if the brain constantly recieving information
RETICULAR ACTIVATING SYSTEM: consits of area with reituclar formaiton wehn activiated bring about increased stimulation of the cerebral cortext
- increased alertness and arousal
- RAS selectively block/allows transmisson of sensory info to cerebal cortext
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SPINAL CORD
-suspended in the vertebral canal, surrounded by meninges
- Continuous with medulla extends from the upper border at the atlas (1st cervical vertebra) lower border of the 1st lumbar vertebra
- nerve impulses from the brain to the organs and tissues descend through the spinal cord
- sensory nerves from organs to tissues enter pass upways in spinal cord to the brain
- some activites = independent of brain
- some controlled at spinal cord level by spinal reflexes
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SPINAL NERVES
Sensory nerve - the spinal cord transmits impulses to the brain and is called sensory, afferent or ascending.
The 2 main sources of sensation are the skin, tendons, muscles, and joints.
The skin has sensory receptors (nerve endings)
stimulated: heat, pain, cold, touch and pressure. Tendons, muscles and joints have proprioceptors and are stimulated by stretch.
Impulses from the eyes and ears are associated with balance, posture, and perception of the body's position in space.
- The nerve impulses from the skin are conducted by 3 neurones (primary, secondary and tertiary) to the sensory area in the opposite hemisphere of the cerebrum where the sensation and location are perceived. Decussation occurs at the level of entry in the spinal cord or in the medulla. The nerve impulses from tendons, muscles and joints are either sent by a 3-neurone system to the sensory area of the opposite hemisphere of the cerebrum or by a 2-neurone system, where the impulse reaches the cerebral hemisphere on the same side.
Motor nerve tracts (efferent or descending) neurons.
Stimulation results in contraction of muscles - skeletal, smooth, cardiac and glandular secretion.
Muscle contraction that moves the joints is mainly under voluntary control, so the stimulus to contract originates at the level of consciousness in the cerebrum.
- But skeletal muscle activity is regulated by output from the midbrain, brain stem and cerebellum. This involuntary activity is associated with co-ordination of muscle activity e.g. in very fine movements and in the maintenance of posture and balance.
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UPPER AND LOWER MOTOR NEURONS
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KNEE JERK REFLEX
3 elements: sensory neurons, interneurons in the spinal cord & lower motor neurons
SIMPLEST REFLEX: involuntary and immediate motor response to sensory stimulus that is protective
- pain initiated by touching hot surfaces with fingers transmitted to the spinal cord by sensory fibres in mixed nerves
- Stimulate many interneurons and lower motor neurons in the spinal cord
- contraction if the muscles of upper limb and removal of fingers
STRETCH REFLEX 2 NERUONS:
- The lower motor neurons in the cell body are stimulated directly by sensory neurons. This type can occur at any point a tendon crosses a joint
- tendon trapped below the bent knee
- Sensory nerve endings in tendons and high muscles are stretched
- impuse passes into spinal cord to body cell of the lower motor neuron in the anterior horn or grey matter
- high muscles contracting and foot kicks forward
AUTOMATIC REFLEXTS: PUPILLARY LIGHT REFLEX
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PERIPHERAL NERVOUS SYSTEM
PSN = nerves in somatic and automatic nervous system 9entering and leaving CNS
- spinal nerves (leave the spinal cord through spaced = intevertebral formainate between vertebrate
- cranial nerves from base of brain and flow through foraminae in the base of the skull
type of nerves: sensory, motor or mixed
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SPINAL NERVES
31 nerves connecting the spinal cord to various body regions
- 8 pairs of cervical nerves
- 12 paired thoracic nerves
- 5 paired lumbar nerves
- 5 paired lumbar sacral nerves
- 1 pair of coccygeal nerves
- There are only 7 cervical vertebrae, but the first cervical nerves leave the vertebral canal between the occipital bone and the atlas.
- The lumbar, sacral and coccygeal nerves leave the spinal cord near its termination at the level of the 1st lumbar vertebra, forming a sheath of nerves that resemble a horse’s tail, the cauda equina.
- These nerves leave the vertebral canal at the appropriate levels.
- Nerve branches also known as rami are when spinal nerves divide into branches.
- Plexuses are when the rami (branches) unite to form large masses of nerves.
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CRANIAL NERVES
I OLFACOTRY
II OPTI
III OCCULOMOTOR
IV TROCHLEAR
V TRIGEMINAL
VI ABDUCENT
VII FACIAL
VIII AUDITORY
IX GLOSSOPHARYNGEAL
X VAGUS
XI ACCESSORY
XII HYPOGLOSSAL
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AUTOMATIC NERVOUS SYSTEM
- The ANS controls involuntary body functions.
- Sympathetic and Parasympathetic. Effector organs are smooth muscle, cardiac muscle, glands (GI secretions).
The efferent motor nerves of the ANS originate from the brain and emerge at various levels, from the midbrain to the sacral region of the spinal cord.
- Each division has 2 efferent neurones between the CNS and effector organs - preganglionic and postganglionic neurones.
Preganglionic fibre: In the autonomic nervous system, fibres from the CNS to the ganglion are known as preganglionic fibres.
- ganglion: A cluster of interconnecting nerve cells outside the brain.
- preganglionic neuron: The nerve fibres that supply a ganglion. The cell body of the preganglionic neuron is in the brain or spinal cord.
- Axon terminals synapse with the cell body of the postganglionic neurons in the autonomic ganglion of the NS.
- postganglionic neurons in an autonomic ganglion outside the NS
- Postganglionic neurons send impulses to the effector organs
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SYMPOATHETIC NERVOUS SYSTEM
- pupils dilate
- saliva and mucous secretion
- vasodilation (skeletal muscles)
- bronchodilation
- peristaslisis reduction
- glucose to glycogen increase
- adrenaline and noradrenaline to blood
- decreased urine output
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PARASYPHATETIC NERVOUS SYSTEM
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ACUTE PAIN
- sensational trigger by anxious stimulus - converting to electrical signals
- signals (action potential) transferred to the spine and then to the brainstem, moving to the cortex
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CLASSIFICATION OF PAIN
- nociceptive pain
- somatic (skin, skeletal muscle, bone, joints, connective tissue
- visceral (internal organs)
NEUROPHATIC PAIN:
- peripheral (abnormal pain from peripheral nerves)
- central (damage to central nerves)
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NOCICEPTORS
Nociception is the neural process involving transmission of a noxious stimulus to the brain via nerve pathways.
Nociceptors are receptors (free nerve endings) in body tissues. They are activated by a painful stimulus. The pain information is transmitted to the central nervous system along axons.
2 types of nociceptors:
High threshold mechanoreceptors
Polymodal nociceptors, which respond to chemicals involved in inflammation:
5-hydroxytryptamine (5-HT); cytokines; bradykinin; prostaglandin; leucotrienes.
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NERVE TRANSMISSION OF PAIN
Nociceptors are the free-nerve endings of nerve fibres.
The 2 main ascending fibre types are Aδ (A delta) and C fibres. These are primary afferent nerve fibres have their cell bodies in the dorsal root ganglia. They terminate in the dorsal horn of the spinal cord.
A delta fibres are large and myelinated – immediate, sharp pain
C fibres are small and unmyelinated – a little slower, dull aching
A beta fibres are large and myelinated – non pain fibres that react to touch e.g. massage
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DORSAL HORN
The dorsal horn is divided into laminae. Lamina II is called the Substantia Gelatinosa.
C fibres terminate in lamina II
Aδ fibres terminate in laminae I and V
Aβ fibres (respond to light touch) terminate in laminae III, IV and V
Aβ fibres also synapse with C fibres in lamina II
Laminae II and V are important for modulation and localisation of pain.
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SECOND ORDER NERUONES TO THE CORTEX
The primary afferent fibres synapse with the second order neurons.
In the spinal cord, the nerve fibres bifurcate into ascending and descending branches.
Second order neurones ascend to the brain via the spinothalamic and spinoreticular tracts.
The information on pain is processed in the thalamus.
The thalamus processes somatosensory information
Third order neurones project to the cortex, where pain is perceived.
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PROCESSING OF PAIN IM THE BRAIN
When the secondary neurone is activated by neurotransmitters from the primary fibre, the nerve impulse goes to a number of areas in the brain.
The somatosensory cortex locates the pain and determines its intensity. It helps us remember pain experiences
The prefrontal cortex helps us decide what to do about our pain
The body responds to pain by increasing heart rate and BP (through the amygdala) and preparing for fight or flight (hypothalamus).
Emotional response from the anterior cingulate cortex
Attention drawn to the pain from the posterior cingulate cortex
The thalamus and insula integrate and co-ordinate all the responses.
Pain also triggers an inhibitory response from the brain – dopamine, noradrenaline, endorphins and serotonin are released from various areas of the brain. These chemicals move to the spinal cord, where they inhibit incoming pain signals.
The pain inhibitory signals can be boosted by various enjoyable activities e.g. exercise, laughter, chocolate and sex
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DESCENDING TRACTS
- The descending tracts modulate pain.
The periaqueductal grey (PAG) and nucleus raphe magnus (NRM) are both in the brainstem.
- they are involved in reducing pain.
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VISCERAL PAIN
Pain arising from internal organs
Poorly localised, due to less nociceptors
Tends to be colicky in nature and often accompanied by nausea.
