Nervous Flashcards
Main functions
- Gather information (sensation)
- Integrate & analyse information
- Respond (behave)
Central nervous system
- Brain
* Spinal cord
Peripheral nervous system
• Peripheral nerves - rest of body (communication)
Sensory pathways
Afferent and efferent
Afferent
Signal towards CNS, away from muscle
Efferent
Signals towards muscle, away from CNS
Neurons
Communicate messages from one part of the body to another
Neuroglia
Support and protect neurons
Neurons comprised of
- Cell body/soma
- Dendrites
- Axon
Dendrites in neuron function
Receive incoming messages
CNS group of cells and bundles called
Nuclei and tracts
PNS group of cells and bundles called
Ganglia and nerves
Cell body in neuron contain
- Ribosomes
- Rough endoplasmic reticulum
- Golgi apparatus
- Mitochondria
Processes of axon in neuron
- Generates and conducts nerve impulses away from the cell body
- Begins at the Axon Hillock which is Trigger Zone for the nerve impulse
- Any long axon is also known as a Nerve Fibre
- Axon terminals end in synaptic knobs containing neurotransmitters
Neurotransmitters
- Chemicals which transmit the message from one neuron to the next cell
- Molecules in axon terminals released in response to a nerve impulse (action potential)
Resting membrane
Negative 70mV inside, positive outside
Neuron communicates through
Action potential traveling through the neuron. They use changes in membrane potential to send signals
Membranes have which pumps
Sodium and potassium
2 potassium in, 3 sodium out
Resting Membrane Potential
Movement of electrical current depends on having a difference in voltage across the neuron membrane
Stages of action potential (mV)
1) Resting state (-70)
2) Depolarisation (up to 30)
3) Repolarisation (down to -90)
4) Hyperpolarization (up to -70)
Action potential
Electrical impulse conducted along axon until reaching axon terminal
Synapse
The functional junction between two neurons, a neuron and muscle or gland
Steps of message sent through action potential
1) Action potential arrives at axon
2) Voltage gated calcium channels opens and calcium enters the axon terminal
3) Calcium entry causes synaptic vesicles to release neurotransmitter by exocytosis
4) Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane
Removal of neurotransmitters
• Diffusion
• Enzymatic degradation
• Reuptake
Important to stop sending messages/contracting
Neuroglia types
Four in the CNS - Ependymal cells
Two in the PNS - Schwann cells
Neuroglia functions
- To surround and support neurons
- To insulate one neuron from another
- To supply nutrients in order to promote neuron health & growth
- To produce chemicals that guide young neurons to make connections
Regions of the brain
- Cerebral Hemispheres
- Diencephalon (thalamus, hypothalamus, pituitary)
- Brain Stem (midbrain, pons & medulla)
- Cerebellum
Gyri
Elevated ridges
Sulci
Grooves between gyri
Fissures
Deeper grooves; separate larger regions
Grey matter of brain
Cortex (outside); comprised of cell bodies, dendrites, unmyelinated axons
White matter of brain
Deep to cortex (inside); comprised of myelinated axons
Regions of cerebral hemispheres
- Frontal lobe
- Parietal lobe
- Occipital lobe
- Temporal lobe
- Insula
Longitudinal fissure
Deep midbrain fissure
Transverse cerebral fissure
Fissure separating cerebellum and central hemisphere
Frontal lobe
Voluntary movement, planning, attention, decision making, personality
Parietal lobe
Body sensation, language comprehension, audiovisual integration
Temporal lobe
Auditory processing
Occipital lobe
Visual processing
Cerebellum
Motor coordination, timing
Motor control & sensory processing is
Contralateral
Thalamus
“Gateway” for sensory information
Brain stem consists of
- Midbrain
- Pons
- Medulla oblongata
Brain stem
Vital functions
Types of white matter
- Commissural fibres
- Association fibres
- Projection fibres
Commissural fibres
Connect gray areas of the 2 hemispheres (also called the ‘corpus callosum’)
Association fibres
Connect areas within the same hemisphere
Projection fibres
Connect hemispheres with lower brain regions or spinal cord
White matter of spinal cord
Outside – myelinated fibres/tracts:
Ascending tracts – take sensory information up to the brain
Descending tracts - take motor information away from brain
Grey matter of spinal cord
Inside – comprised of cell bodies, dendrites, small unmyelinated axons
Protection of the Central Nervous System
- Bones
- Meninges
- Cerebrospinal Fluid
- Blood Brain Barrier
Dura Mater
Deep meningeal layer forms folds to anchor the brain and protect large veins
Meninges consist of
Three connective tissue membranes that lie just external to the CNS organs
• Dura Mater (outside)
• Arachnoid Mater (middle)
• Pia Mater (inside)
Arachnoid Mater
Web-like extensions that branch through the Subarachnoid Space which contains cerebrospinal fluid and the largest blood vessels serving the brain
Pia Mater
Delicate connective tissue that adheres to the brain
Cerebrospinal Fluid
Provides buoyancy, makes it light and stops it collapsing in on itself, provides cushioning / shock absorption, nourishes the brain and spinal cord, carries chemical signals such as hormones, sleep and appetite molecules/ optimum environment for neuronal impulses
Blood Brain Barrier
Regulates exposure to numerous chemical substances flowing within the bloodstream from accessing delicate brain tissue
Sections of nerves within spine
1) Cervical spinal nerves (C1-C8)
2) Thoracic spinal nerves (T1-T12)
3) Lumbar spinal nerves (L1-L5)
4) Sacral spinal nerves (S1-S5)
Pairs of cranial nerves
12
Pairs of spinal nerves
31
A spinal nerve consists of:
- Sensory fibres are afferent neurons enter via the posterior or dorsal nerve root
- Motor fibres are efferent neurons leave via anterior or ventral nerve root
Reflexes consist of
1) Receptor
2) Sensory neuron
3) Integration centre
4) Motor neuron
5) Effector
Somatic reflex
Contraction of skeletal muscle, so there is awareness
Autonomic or visceral reflex
Involves smooth muscle and glands, so there’s no awareness
Cranial reflex
Brainstem involved
Spinal reflex
Spinal cord involved
Ipsilateral reflex
Sensory nerve enters the spinal cord on the same side as the motor nerve leaves it (response on same side as stimulus)
Contralateral reflex
Sensory impulses enter on one side of the spinal cord and motor nerves leave on the other side (both sides of the body may respond – e.g. pupillary reflex)
Crossed extensor reflex is important for
Maintaining balance
From sensation to perception
1) Receptor level
2) Circuit level
3) Perceptual level
Receptor level
Sensory receptors detect a stimulus & transmit the information into the spinal cord via the afferent nerve fibre
Circuit level
Sensory information travels up the spinal cord in the ascending tracts (fibres may cross over along the way) to the thalamus
Perceptual level
Information is sent by the thalamus to the correct area of the somatosensory cortex to precisely identify the location of the stimulus
Parasympathetic
"Rest and digest" • Constrict pupils • Stimulate saliva • Slow heartbeat • Constrict airways • Stimulate activity of stomace • Inhibit release of glucose, stimulate gallbladder • Stimulate activity of intestine • Contract bladder • Promote erection of genitals
Sympathetic
"Fight or flight" • Dilate pupils • Inhibit saliva • Increase heart beat • Relax airways • Inhibit activity of stomach • Stimulate release of glucose, inhibit gallbladder • Inhibit activity of intestines • Secrete epinephrine and norepinephrine • Relax bladder • Promote ejaculation and vaginal contraction
Cerebrospinal fluid circulation
1) Cerebrospinal fluid is produced by choroid plexus of each ventricle
2) Cerebrospinal fluid flows through ventricles and into subarachnoid space via the median and lateral apertures. Some cerebrospinal fluid flows through the central canal of the spinal cord
3) Cerebrospinal fluid flows through subarachnoid space
4) Cerebrospinal fluid is absorbed into the dural venous sinuses via the arachnoid villi
