Nervous system Flashcards
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
Describe unipolar neuron
E.g. Primary sensory neurons
- Cell bodies in ganglia (found close to intervertebral foramen)
Describe bipolar neuron
One axon and one dendrite
E.g. Specialized sensory neurons
- Found in retina
Describe Multipolar neuron
One axon and multiple dendrites
- E.g. Majority of neurons in brain
- Also, motor neurons
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
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
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
Describe astrocytes
Provide structural support
Supply nutrients
Maintain ionic environment (remove K+)
Neurotransmitter uptake
Repair of the nervous system
- Form barrier around vessels
Describe Oligodendrocytes
Production and maintenance of myelin sheath
- One oligodrocyte myelinates multiple axons
Describe microglia
Immune cells
- Phagocytic (like macrophages)
- Cytotoxic (releasing H2O2)
- Promote repair
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
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
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
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
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
Describe the hypothalamus
The hypothalamus is important in homeostasis
Sits below thalamus
Controls:
- Autonomic nervous system
- Endocrine system
Describe the brainstem
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
The cerebellum coordinates complex muscular movements
Sits behind the brainstem
Describe the spinal cord
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
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
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
All peripheral nerves arise from:
Brain or brainstem as Cranial nerves
Spinal cord as Spinal nerves
Describe spinal nerves
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
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
