Nervous System Flashcards
Central Nervous System (CNS)
- Command centre
- Brain + spinal cord
- Processes + integrates information
Peripheral Nervous System (PNS)
- Consists of:
1) Cranial nerves - to/from brain
2) Spinal nerves to/from spinal cord - 2 divisions of PNS:
1) Sensory/afferent division
Peripheral Nervous System Divisions
1) Sensory/afferent division
- Has sensory receptors that detect stimuli (changes in the internal or external environments)
- Nerves convey impulses TOWARD CNS
2) Motor/Efferent division
- Nerves convey impulses AWAY from CNS
- Innervates (supplies nerves to) effectors = muscles + glands (endocrine or exocrine)
Relationship between CNS and PNS
Look at diagram
Nervous System Organization
Diagram
Neurons (Nerve cell type)
- Conduct impulses
- Make up CNS + PNS
- Mostly amitotic (irreplaceable) exceptions = taste, olfaction, memory
- Structures:
1) Cell body
2) Processes from cell body
a) Dendrites
b) Axon
Cell body (Neurons)
- Typical organelles
- RER called Nissl bodies
- Groups/clusters in CNS = nuclei (grey matter)
- Groups/clusters in PNS = ganglia
Dendrites (Neurons)
Receive incoming messages + relay to cell body
Axon (Neurons)
- Carries impulses away from cell body
- Axon hillock - where axon meets cell body
- Axon terminal - typically branched with synaptic end bulbs (enlarged tips)
Myelinated Axon
- Myelinated - wrapped in many layers of cell membrane from Schwann cells (PNS) or oligodendrocytes (CNS)
- Electrical insulation
- Gaps in myelin sheath are called nodes of Ranvier
- Myelinated axon bundles in:
1) CNS = tracts (white matter)
2) PNS = nerves (know the difference)
Unmyelinated Axon
No myelin
Neuroglia (Glial cells) (Nerve Cell Type)
- Support neurons = can undergo mitosis (prone to cancer - brain tumour)
CNS Neuroglia
1) Oligodendrocytes
2) Microglia
3) Astrocytes
4) Ependymal Cells
Oligodendrocytes (CNS neuroglia)
Produce myelin around axon
Microglia (CNS neuroglia)
- Protective – become phagocytic if detect infected, dead or damaged neurons (because immune cells can’t enter CNS)
Astrocytes (CNS neuroglia)
- Surrounded blood capillaries to form part of blood brain barrier (BBB)
- Help control capillary permeability
Ependymal Cells (CNS neuroglia)
- Neural epithelium
- Line brain ventricles + central canal of spinal cord
- Secrete cerebrospinal fluid (CSF) + circulate it (cilia)
PNS Neuroglia
1) Schwann Cells
- Form myelin around axons in PNS
2) Satellite Cells
- Surround neuron cell bodies ganglia
- Protection and support
Neuron Classification
1) Structural/ Anatomical Types:
- Based on number of processes coming off cell body
a) Unipolar
b) Bipolar
c) Multipolar
2) Functional Types:
- Based on direction of impulse conduction
a) Sensory/Afferent neurons
b) Interneurons
c) Motor/Efferent neurons
Unipolar
- 1 process the divides into two: central + peripheral
- Peripheral end has dendrites = sensory receptors (pain, touch, etc) - reminder is axon
- Always sensory
Bipolar
- 2 processes: 1 axon, 1 process with dendrites
- Sensory = retina, nose (olfaction)
Multipolar
- 3 or more processes: 1 axon, many dendrites
- All interneurons + motor neurons
Sensory/Afferent Neurons
- Mostly unipolar
- From sensory receptors to CNS
Interneurons
- Within CNS (between sensory + motor)
- 99% of neurons (mostly multipolar)
Motor/Efferent Neurons
- CNS to effectors (all multipolar)
Neuronal Junctions (Synapses)
1) Neuronal Junction:
- Neuron to Neuron
- Can be chemical (use neurotransmitters) or electrical (ions)
2) Neuromuscular Junction:
- Motor neuron to skeletal muscle cell
3) Neuroglandular Junction:
- Motor neuron to smooth or cardiac muscle, or a gland
Chemical Neuronal Synapses
- Most common
- Structures:
1) Presynaptic Neuron - Neuron bringing impulse
- Has axon terminal with synaptic end bulbs
- Inside end bulb = synaptic vesicles containing neurotransmitter (nt)
- Presynaptic membrane (cell membrane facing space)
2) Synaptic Cleft - Space between neurons
3) Postsynaptic Neuron - Receives the signal
- Has postsynaptic membrane = cell membrane of dendrites or cell body with receptors for nt
Central Nervous System: Protective Features
1) Bone
2) Meninges
3) Cerebrospinal Fluid (CSF)
4) Blood-Brain Barrier (BBB)
5) Cerebral Arterial Circle
Bone
- Skull and vertebral column
Meninges
- CT around brain + spinal cord
- Layers:
1) Dura Mater
2) Arachnoid Mater
3) Pia Mater - Meningitis = inflammation of meninges
Dura Mater (Outer)
- Brain = 2 fused layers - separated in some places to form spaces = venous (dural) sinuses - contain blood
- Spinal cord - 1 layer
- Deep to dura mater = subdural space - filled with ISF
- Superficial to dura mater = epidural space (spinal cord only) - filled with fat, blood vessels, CT, etc
Arachnoid Mater (Middle)
- Avascular
- Subarachnoid space:
~contains cerebrospinal fluid (CSF)
~ Web-like strands of CT secure it to Pia mater (below) - Has arachnoid granulations (brain only)
~ Projections into dural sinuses
~ CSF enters granulations to return to blood
Pia Mater (Inner)
- On surface of CNS (brain and spinal cord)
- Vascular
Cerebrospinal Fluid (CSF)
- Surrounds brain + spinal cord
- In brain ventricles + central canal of spinal cord
- Ventricles:
~ Spaces inside brain (filled with CSF)
~ 2 lateral ventricles (1st and 2nd) - in cerebrum
~ 3rd ventricle - in diencephalon
~4th ventricle - surrounded by pons, medulla oblongata, cerebellum - Central canal:
~ Space in spinal cord - Cushions CNS - brain buoyant
- Formed from blood plasma (similar composition)
- Produced by choroid plexuses (blood capillaries) found in each ventricle
- Circulation: LOOK AT DIAGRAM
Blood-Brain Barrier (BBB)
- 2 cell types:
1) Endothelial cells (of capillaries) with tight junctions
2) Astrocytes - foot processes wrap around endothelial cells - Selectively Permeable
- Allows: glucose, fat soluble material to cross
- Not toxins, antibiotics etc
- In most parts of brain except:
Posterior pituitary, hypothalamus, vomiting centre
Cerebral Arterial Circle
Cerebral arteries form circle at base of forebrain
- Circles pituitary gland and optic chiasma (where optic nerves cross)
- Unites the 2 major blood supplies to the brain (anterior and posterior)
- Provides an alternate toute for blood if vessels blocked
Blood flow to Brain
Diagram
Blood Return From The Brain
Cerebral Arteries Capillaries Cerebral Veins Dural Sinuses Superior Vena Cava
Cerebrum (Forebrain)
= right and left cerebral hemispheres
- Lobes (named after overlying bones)
1) Frontal
2) Temporal
3) Parietal
4) Occipital
5) Insula - deep to temporal lobe
Structure Features of the Cerebrum
1) Fissures = deep groves
2) Gyri = ridges
3) Sulci = Shallow Grooves (separate gyri)
Fissures
1) Longitudinal Fissure
- Separates right and left hemispheres
2) Transverse Fissure
- Separates cerebellum + cerebrum
3) Lateral Fissure
- Separates temporal lobe from rest of cerebrum
Gyri
Examples:
- Postcentral gyrus in parietal lobe
- Precentral gyrusin frontal lobe
Sulci
Example:
- Central sulcus - between frontal and parietal lobes
Layers to the Cerebrum
1) Cerebral Cortex
2) Tracts (white matter)
3) Basal Nuclei
Cerebral Cortex
- 2-4 mm thick, grey matter
- Has functional areas:
1) Motor Areas
2) Sensory Areas
3) Association Areas
4) Others
Motor Areas (Cerebral Cortex)
- All in frontal lobe
- Control skeletal muscle movement
- 3 regions:
1) Primary motor area (pre central gyrus)
2) Premotor Area
3) Broca’s - language
Sensory Areas (Cerebral Cortex)
1) General sensory area (pain, temp, touch, pressure)
- Postcentral gyrus in parietal lobe
2) Vision
- Occipital lobe
3) Auditory + Olfaction
- Temporal lobe
4) Taste + Visceral Sensation (e.g. full bladder)
- Insula
Association Areas (Cerebral Cortex)
Recognize into from memories - parietal, occipital, temporal lobes
Others (Cerebral Cortex)
- Memory - Temporal lobes
- Conscious intellect (personality, learning, ideas, judgement etc)
- Prefrontal cortex
Tracts (white matter)
1) Association Tracts
- Form gyrus to gyrus in same hemisphere
2) Commissural Tracts
- Form gyrus to gyrus in opposite hemispheres
- E.g. corpus callosum
3) Projection Tracts - run vertically (brain to spinal cord/ spinal cord to brain)
Basal Nuclei
- Paired masses of grey matter (within the white matter)
- Involved in control of skeletal muscle movement
Diencephalon
- All gray matter
1) Thalamus - 2 lobes connected by intermediate mass (bridge of grey matter across 3rd ventricle)
- Relay station for most sensory impulses to cortex
2) Hypothalamus - Inferior to thalamus, above pituitary
- Major regulator of the internal environment (visceral control)
- e.g. blood pressure, heart rate
Midbrain
- Connects pons + diencephalon
- Contains cerebral aqueduct
- Anterior portion = cerebral peduncles (projection tracts)
- Posterior portion = 4 nuclei = corpora quadrigemina
~ 2 superior colliculi - visual reflexes
~ 2 inferior colliculi - hearing + auditory reflexes
Hindbrain
Includes: 1) Pons 2) Medulla Oblongata 3) Cerebellum NOTE: Brain Stem = midbrain, pons, medulla
Pons (Hindbrain)
- Anterior to cerebellum
- Contains:
Tratcs between brain + spinal cord + tracts to/from cerebellum
Pontine respiratory centres
Medulla Oblongata (Hindbrain)
- Inferior to pons
- Ends at foramen magnum
- 2 bulges called pyramids = large motor tracts (= part of corticospinal tracts)
- Just above spinal cord = decussation of pyramids (tracts cross over)
- 3 vital centres (nuclei) in medulla:
1) Cardiac
2) Vasomotor (blood vessels)
3) Respiratory - Several non-vital centres - for swallowing, sneezing, vomiting
Cerebellum (Hindbrain)
- Posterior to pons, medulla
- Has folds similar to gyri = folia - cortex (grey matter(
- Arbor vitae (deep to cortex, anterior cerebellum) = white matter
- Coordinates skeletal muscle contraction - posture, balance
Limbic System (Functional Systems)
- Nuclei in cerebrum + diencephalon
- Regulates emotions + emotional behaviours (laughing, crying etc)
- Contains areas involved in memory (memories evoke emotional responses)
Reticular Formation (Functional Systems)
- Nuclei in brain stem
- Cortex, thalamus + hypothalamus involved - together form RAS = Reticular Activating System
- Regulates alertness + attention - filters stimuli + only sends new/unusual signals to other brain areas
- Sleep results when inhibited
- If damaged = coma
Spinal Cord (Structure Overview)
- Foramen magnum to level of lumbar vertebrae L1?l2 (conus medullar is)
- Nerves continue down from spinal cord through vertebral foramina as caudal equina (“horse’s tail”) - exit at intervertebral foramina
- Filum terminale
~ CT= extension of Pia mater - anchors conus medullar is of spinal cord to coccyx
~ Location where CSF samples taken
Spinal Cord (Cross-sectional Structure)
1) Anterior median fissure + posterior median sulcus
2) Central Canal
3) Gray Matter
4) White Matter
Anterior Median Fissure + Posterior Median Sulcus
- Separate cord into right and left halves
Central Canal
- Contains CSF
Gray Matter
- Cell bodies + dendrites of motor neurons, interneurons
- H-shaped
~ Cross bar = gray commissure
~ Horns
1) Dorsal Horn = sensory
2) Lateral Horn = motor
3) Ventral Horn = motor
White Matter
- Myelinated axons = ascending (sensory) and descending (motor) tracts
- Forms columns:
1) Dorsal Column
2) Lateral Column
3) Ventral Column
Spinal Cord Function in the CNS
- Carries sensory and motor impulses
- Produces reflexes - Fas, predictable, automatic responses to changes in the environment (E.g. withdrawal reflex)
Cranial Nerves (PNS) Pairs)
- 12 pairs in total I. Olfactory II. Optic III. Oculomotor IV. Trochlear V. Trigeminal VI. Abducens VII. Facial VIII. Vestibulocochlear IX. Glossopharyngeal X. Vagus XI. Accessory XII. Hypoglassal
Cranial Nerves are associated with the following brain regions:
-Forebrain: Olfactory, Optic - Midbrain Oculomotor, Trochlear - Pons: Trigeminal, Abducens, Facial, Vestibulocochlear - Medulla Oblongata Glossopharyngeal, Vagus, Accessory, Hypoglossal
Cranial Nerves Extra info
1) 2 pairs = only sensory neurons
- I + II
2) 1 pair = mainly sensory
- VIII
3) 9 pairs = mixed nerves
- Carry both sensory + motor neurons
- Motor neurons = cell bodies in brainstem nuclei
- Sensory neurons = cells bodies in ganglia of PNS
- E.g. Trigeminal (V)
Motor function = chewing
Sensory function = conveys general sensations (touch, pressure, pain, temperature etc) from face to CNS
Spinal Nerves (PNS)
- 31 pairs = all mixed nerves
8 cervical
12 thoracic
5 Lumbar
5 Sacral
1 Coccygeal - Exit via intervertebral foramina (except 1st - between atlas + occipital bone)
- Each has 2 points of attachment to spinal cord: 1) Dorsal Root and 2) Ventral Root
- Spinal Nerves = joining of dorsal + ventral roots - immediately divides into branches = rami: 1) Dorsal Ramus 2) Ventral Ramus 3) Rami Communicantes
Dorsal Root
- Sensory; cell bodies in dorsal root ganglion (Have diagram)
Ventral Root
- Autonomic and somatic motor neurons; cell bodies in ventral or lateral horn
Dorsal Ramus
Innervates skin + muscles of back
Ventral Ramus
- Forms thoracic nerves (t2-T12) OR further branch + join up forming nerves plexuses (= nerve networks)
Rami Communicantes
- Connect ventral ramps to sympathetic trunk
- Contain autonomic nerve fibres (neurons)
Cervical Nerve Plexus
- Formed by spinal nerves C1-C5
- Important nerves arising - Phrenic (innervates diaphragm)
Brachial Nerve Plexus
- Formed by spinal nerves C5-C8, T1
- Important nerves arising -Axillary, Radial, Ulnar median, Musculocutaneous
Lumbar
- Formed by spinal nerves L1-L4
- Important nerves arising: -Femoral
Sacral
- Formed by spinal nerves L4-S4
- Important nerves arising: - Sciatic = divides into tibial + common fibular
Cross-section of a Nerve (PNS)
1) Nerve = Epineurium - around whole nerve (CT)
2) Axon = Perineurium - around fascicles (CT)
3) Fascicle = Endoneurium - around axon + myelin (CT)
Peripheral Nervous System: Sensory (Afferent) Division
Consists of:
1) Receptors
a) Location
b) Type of stimulus
c) Structure of Receptor
2) First Order Neurons = sensory neurons
Receptors of Sensory Division
- Detect changes in environment
- Classified by:
a) Location
b) Type of Stimulus Received
c) Structure of Receptor
Exteroceptors (Location)
- Stimulus in external environment = receptors at body surface e.g. Touch, most special senses
Interceptors (Location)
- Stimulus in internal environment (in viscera, blood vessels etc.)
Proprioceptors (Location)
- Located in joints, skeletal muscles etc.
- Monitor body position (stretch receptors, muscle spindles) - balance + movement
Mechanoreceptors (Type of Stimulus Received)
- Mechanical stimuli (e.g. pressure, touch, hearing)
Thermoreceptors (Type of Stimulus Received)
-Temperature
Chemoreceptors (Type of Stimulus Received)
- Chemical
Photoreceptors (Type of Stimulus Received)
- Light
Nociceptors
- Pain
Structure of Receptor (General Senses Only)
1) Free Nerve Endings
- Terminal dendrites of unipolar sensory neurons
- E.g. pain, root hair plexus
2) Encapsulated nerve endings
- Terminal dendrites enclosed in CT
- E.g. Messiner’s + Pacinian Corpuscles
First Order Neurons = Sensory Neurons
- Unipolar neurons attached to or associated with receptor
- Axon located in cranial/ spinal nerves to CNS
- Cell bodies in:
a) sensory ganglia of cranial nerves
b) Dorsal root ganglia of spinal cord - Axon terminals nuclei
a) Brain nuclei
b) Dorsal horn of spinal cord
