Immune cells - Phagocytic (like macrophages) - Cytotoxic (releasing H2O2) - Promote repair

Nervous system Flashcards by Rathushan Yogarasa

Describe a neuron

functional unit of the nervous system
Soma/cell body 
 Contains the nucleus
 Synthesis of proteins/ion channels
- Important for cellular metabolism

Dendrites (dendritic tree)
Receives inputs
Convey information towards soma
- Large surface area (spines) for synapse formation

Axon hillock
- Origin of the axon
Very excitable

Axon/nerve fibre
- Transmits action potential
Usually only one (although often branches)

Axon terminals
Synapse on other neurons, effector organs or forms specialized ending

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Describe unipolar neuron

E.g. Primary sensory neurons

Cell bodies in ganglia (found close to intervertebral foramen)

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Describe bipolar neuron

One axon and one dendrite

E.g. Specialized sensory neurons

Found in retina

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Describe Multipolar neuron

One axon and multiple dendrites

E.g. Majority of neurons in brain
Also, motor neurons

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What are the two types of neutrons in terms of function

Afferent – Carry information to central nervous system

Efferent – Carry information away from central nervous system

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Describe axons

Can be myelinated (>1µm diameter)

Saltatory conduction:

Very rapid (up to 120m/s)

Action potential passes from node to node

Can be unmyelinated (<1µm diameter)

Very slow (<1.5m/s)
E.g. Pain fibre

Larger axon diameter = faster conduction

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Describe synapses

Junction between axon terminal and target cell
- E.g. neuron (dendrite) or muscle (neuromuscular junction)

Chemical synapses:
Majority of synapses are chemical synapses

Use neurotransmitters (e.g. acetylcholine)

Depolarisation of presynaptic membrane opens Ca+ channels
Vesicles fuse to membrane and release neurotransmitter

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Describe astrocytes

Provide structural support

Supply nutrients

Maintain ionic environment (remove K+)

Neurotransmitter uptake

Repair of the nervous system

Form barrier around vessels

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Describe Oligodendrocytes

Production and maintenance of myelin sheath

One oligodrocyte myelinates multiple axons

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Describe microglia

Immune cells

Phagocytic (like macrophages)
Cytotoxic (releasing H2O2)
Promote repair

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Discuss the neuroglia of the PNS

Schwann cells are the neuroglia of the PNS

Myelinate axons (spiral wrapping)

Important for regeneration
(provide substrate for axon to grow along)

One Schwann cell myelinates one axon

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Describe the central nervous system

Brain is divided into forebrain, midbrain and hindbrain

Made up of grey and white matter

FOREBRAIN:
Cerebral hemispheres
Thalamus
Hypothalamus

MIDBRAIN:

HINDBRAIN:
Cerebellum
Pons
Medulla

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Describe the forebrain

The cerebral hemispheres are highly developed

The outer grey matter layer is the cerebral cortex

Function is to process motor and sensory information

Although, 80% of cortex functions in cognition

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Describe the lobes of the cerebral hemisphere

Frontal lobe: Primary motor cortex

Parietal lobe: Primary somatosensory cortex (pain, touch and proprioception)

Temporal lobe: Primary auditory cortex + olfaction

Occipital lobe:
Primary visual cortex

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Describe the thalamus

The thalamus is the relay centre of the brain

Paired structure

Centrally located

All sensory information (except smell) is relayed via the thalamus

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Describe the hypothalamus

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The hypothalamus is important in homeostasis

Sits below thalamus

Controls:
- Autonomic nervous system

Endocrine system

Describe the brainstem

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The brainstem is formed by the midbrain and hindbrain

Connects cerebral cortex to spinal cord
Controls respiration and the cardiovascular system

damage will most likely be fatal

Describe the hindbrain

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The cerebellum coordinates complex muscular movements

Sits behind the brainstem

Describe the spinal cord

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Extends from atlas to first lumbar vertebra (L1)

Sits within vertebral canal

Conveys information from PNS to brain (sensory)

Conveys information from brain to PNS (motor)

Involved in reflexes

Segmentally organised

Inner core of gray matter
Neuronal cell bodies

Outer, white matter
Myelinated axons
Convey information to/from brain

Describe the peripheral nervous system

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Connects CNS with periphery

Nerve supply to muscles, glands, skin, vessels, viscera

Peripheral nerves convey motor, sensory and autonomic axons

Describe the somatic component of the PNS

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Comprises:
Somatic motor neurons
- Axons of the motor neurons that supply the skeletal muscles

Somatosensory neurons
- Axons of the primary sensory neurons

Carries information about external environment (Exteroceptive)
Carries information from within body (Proprioceptive)

Describe the origin of peripheral nerves

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All peripheral nerves arise from:

Brain or brainstem as Cranial nerves

Spinal cord as Spinal nerves

Describe spinal nerves

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Spinal nerves provide motor and sensory supply to whole body, except head and neck

Also sympathetic supply to whole body

Excellent segmental organisation

One pair of spinal nerves at each vertebrae

Dorsal and ventral roots merge to form spinal nerves

Mixed nerves (motor, sensory and sympathetic)

Exit through intervertebral foramen

Describe the spinal nerve organisation

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8 cervical: Upper limb/head/neck

Note, only 7 cervical vertebrae

C1-7 exit above vertebrae, C8+ exit below

12 thoracic: Thorax/abdomen

5 lumbar: Pelvis/lower limb

5 sacral: lower limb

1 coccygeal nerve

Describe the dorsal and ventral roots

Nerve roots connect spinal nerves to the spinal cord Ventral root – Efferent (motor/sympathetic) Dorsal root – Afferent (sensory) Nerve roots sit within vertebral canal

Describe the primary rami

Spinal nerves divide into: - Dorsal/posterior primary ramus - Ventral/anterior primary ramu

Describe the dorsal primary ramus

Supplies: Skin over paravertebral gutter Erector spinae muscles Facet joints of vertebral column

Describe the ventral primary ramus

Supplies rest of the body (i.e. skin and musculoskeletal system) Much larger nerve

Describe the map of ventral primary rami

Form intercostal nerves and four nerve plexuses A nerve plexus is where ventral primary rami merge Forms nerves contain axons from multiple spinal nerves Important for innervation to limbs (large muscle groups)

Describe dermatomes and myotomes

Segmental organization of spinal nerves results in dermatomes and myotomes Dermatome: - An individual area of skin innervated by a single spinal nerve (primary ramus) Myotome: An individual muscle group innervated by a single spinal nerve (primary ramus)

Describe the Embryonic development of dermatomes and myotomes

Dermatomes and myotomes develop from somites (mesoderm) during embryonic week 3 Somites are paired blocks that form horizontal bands One pair of spinal nerves (ectoderm) grows into one pair of somites

Discuss the clinical importance of dermatomes

Loss/altered sensation/pain from dermatome indicates injury to spinal cord, nerve root or spinal nerve - Easy to determine location of injury from dermatomes E.g. loss of sensation from skin over umbilicus may indicate damage to…… Also, visceral (organ) pain can be referred to skin (dermatomes) as cutaneous pain E.g. Diaphragm irritation referred to shoulder (C3-C5 dermatomes)

Describe myotomes

Conserved in thorax Intercostal muscles supplied by intercostal nerves (T1-T11) More complicated in limbs (more than one spinal nerve innervating muscle groups)

Describe the autonomic component of PNS

Involuntary part of the peripheral nervous system Involuntary control: - Regulates operation of the internal organs - Maintains internal environment Two main divisions of the ANS: SYMPATHETIC PARASYMPATHETIC

Discuss the origin of ANS

Parasympathetic Origin: Brainstem Sympathetic Origin: Thoracic/lumbar spinal cord Parasympathetic Origin: Sacral spinal cord

Describe the sympathetic trunk

Interconnected paravertebral ganglia Sits either side of vertebral column All preganglionic sympathetic axons enter the sympathetic trunk Postganglionic axons exit via spinal nerves to - musculoskeletal system (Constriction of blood vessels, piloerection, sweating) Postganglionic axons exit through branches to heart, lungs or head (Bronchodilation, increase cardiac output, pupil dilation, increase sweating)

Describe the prevertebral ganglia

Some preganglionic axons enter splanchnic nerves and pass to prevertebral ganglia in abdomen Postganglionic axons project to - abdominal/pelvic organs (Inhibit peristalsis/gastric secretions, stimulates glucagon release)

Describe the Cranial parasympathetic

Cell bodies of preganglionic neurons in brainstem Ganglia located close to effector organs

Describe sacral parasympathetic

From sacral part of spinal cord Preganglionic axons exit via pelvic splanchnic nerves Synapse with postganglionic axons on the pelvic organs

Nervous system Flashcards

(39 cards)