Week 5: Central Nervous System Flashcards
Anatomical Divisions of the brain?
- Cerebrum: Left and right hemispheres. Left controls RHS, right controls LHS
- Diencephalon, deep within the brain as deep as you can go centrally: Thalamus, Hypothalamus
- Brainstem, inferiorly: Midbrain, Pons, Medulla oblongata
Cerebellum: Mini brain at the back, posterior and inferior
Structure of the cerebral hemisphere?
- The outermost surface/superficial layer of the brain is called the cerebral cortex (cortex= outside, medulla=inside)
- It has a convoluted (wiggly) surface with elevated ridges called gyri (one=gyrus) and shallow grooves called sulci (one=sulcus)
- Each hemisphere contains four distinct lobes: Frontal lobe, parietal lobe, temporal lobe and occipital lobe
Each lobe comprises of a primary functional area and a larger association area
Primary functional areas of the brain lobes?
- Frontal lobe, dorsal end: Primary motor cortex e.g. relays signals to control bodily movements, voluntary movement
- Parietal lobe: Primary somatosensory cortex e.g. receives and interprets sensory information, receiving and interpreting sensory information
- Temporal lobe, superior portion of temporal lobe: Primary auditory cortex e.g. processing all sounds and tones, hearing
- Occipital lobe, most dorsal part: Primary visual cortex e.g. receives and interprets visual information, vision
Grey and White Matter of the brain?
- Grey matter contains the cell bodies (soma) of neurons and unmyelinated axons
- Generally located on the periphery, however, some deep parts of the brain also contain grey matter called nuclei
- White matter contains the axons of neurons (white because of myelin sheath), sometimes referred to as tracts of fiber tracts
White =myelin sheath of oligodendrocytes is white - Grey is generally located on the outside
- Contains cell body’s of neurons
- Area called cerebral cortex and cerebellar cortex
- Some deep parts of the brain have grey matter called nuclei
White matter located internal contains axons of neurons, also called tracts, fiber tracts
Grey matter: Motor and somatosensory Homunculi
- The primary motor cortex (pre-central gyrus) and the primary somatosensory cortex (post-central gyrus) are organized into homunculi
- A homunculus is a distorted-looking image of a person
- Certain body parts are enlarged to reflect the relative size of the areas of the brains motor cortex and somatosensory cortex that are devoted to each of those body parts
e.g. more nervous tissue is devoted to the control of the face than the forearm
Grey and white matter of the spinal cord:
- Opposite orientation in the spinal cord, where the white matter is seen in the periphery and the grey matter is located centrally (deep)
- Shape of grey matter of the spinal cord resembles the letter H or a butterfly
- Grey matter arranged into horns - dorsal, ventral and lateral
White matter arranged into columns- dorsal, anterior and lateral
Structure of the Spinal Cord?
- Column of nervous tissue that connects the brain and PNS
- Enclosed in the vertebral/spinal canal or the vertebral column
- Originates as an extension of the brainstem (medulla oblongata) and continues down until L1/L2 vertebra where it terminates as the conus medullaris
- Distal end of the spinal cord is anchored to the coccyx via a thin thread of connective tissue called the filum terminal
- Inferior to the conus medullaris where the nervous tissue no longer resembles a thick column, many spinal nerves form a structure called the cauda equine
- Filum terminale runs through the center
Features of the spinal cord?
- Regions of the spinal cord take their name from the different regions of the vertebral column they are (corresponding to areas of the body)
- 8x cervical segments
- 12x thoracic segments
- 5x lumbar segments
- 5x sacral segments
- 1x coccygeal segment
Each segment has a left and right spinal nerved (PNS) attached to it (pair of spinal nerves)
Enlargements of the spinal cord?
- There are 2 well defined enlargements in the spinal cord: One located at each the cervical and lumbar levels
- Spinal nerves that are present here control the upper (cervical) and lower (lumbar) limbs
- More neurons enter/exit here as nervous control of the limbs requires many more neurons
More cell bodies in the grey matter
Grey matter of the spinal cord?
- Grey matter contains neuronal cell bodies arranged by function:
- Dorsal/posterior horns containing interneurons that receive input from both visceral and somatic sensory neurons (sensory neuron cell bodies in dorsal root ganglion)
- Lateral horns contain autonomic (involuntary) motor neuron cell bodies
Ventral/anterior horns contain somatic (voluntary) motor neuron cell bodies
White matter of the spinal cord?
- White matter contains neuronal cell axons
- Axon= signal transmission
- White matter contains both myelinated and unmyelinated axons, organized into columns (form nerve tracts)
White matter is what links the spinal cord and the brain
Neural pathways and tracts:
What is a neural pathway?
- Grey matter of the spinal cord has functional areas e.g. somatic motor neuron cell bodies are found in the ventral horn
- Brain cortex has functional areas e.g. primary motor cortex
- It makes sense to organize neurons coming from the same place, carrying the same type of information to the same brain region together
Putting these neurons together creates a pathway - Connect body to the brain and involve CNS and PNS
- Pathways involve multiple neurons most pathways cross from one side to the other - decussate
Tract is the term for the section of pathways found only within the CNS
Ascending neural pathways?
- Ascending pathways travel from body up into the spinal cord (via spinal nerves) and up to the brain
- They carry sensory information that requires processing by the brain e.g. touch
- Pathway involved three neurons; First order neuron (sensory neuron), second order neuron (interneuron), third order neuron (interneuron)
- Information travels from the body to the brain
- Sensory information
- 3 neurons: First order (general somatic afferent)
- Second order neuron (interneuron)
Third order neuron (interneuron)
Descending neural pathways?
- Descending pathways travel from the brain down the spinal cord and out to the body via spinal nerves
- They carry motor information to muscles of the body
Pathway involves two neurons: Upper motor neuron, lower motor neuron - Information travels from the brain to the body
- Motor
- 2 neurons involved
- Upper motor neuron and lower motor neuron
- They carry motor information to muscles of the body
Neural pathway vs neural tract?
- Pathways connect the body to the brain - so involved PNS and CNS - and involve multiple neurons
- e.g. there is always at least one synaptic relay (where one neuron synapses on another)
- Tract is the term for a section of a pathway found only within the CNS
- e.g. controlling the movement of your little finger involved a descending somatic motor pathway, travelling from the brain (CNS) to the little finger (PNS) via multiple neurons. However the section of this pathway between the brain and spinal cord (CNS only) is called the corticospinal tract and only involved one motor neuron
Decussation?
- MOST neural pathways cross from one side of the body to the other (decussate) within the CNS
- Either cross in the medulla or spinal cord
- This is why the left side of the body is controlled by the right hemisphere of the brain and vice-versa
- Decussation can occur in varying locations depending on the pathway involved
- Cranial decussation occurring at the medulla oblongata
- Spinal decussation occurring within the spinal cord
Spinothalamic (anterolateral) pathway?
- Ascending pathway/sensory
- Anterior tract carries sensory information relating to crude touch
- Lateral tract carries sensory information relating to pain and temperature
Pathway/where do the tract neurons go:
- First order neuron: Pseudo unipolar sensory neuron synapses in dorsal horn of grey matter of the spinal cord
- Second order neuron: Interneuron decussates in the spinal cord and ascends in the anterior or lateral spinothalamic tract to the thalamus
Third order neuron: Interneuron travels from the thalamus to the primary somatosensory cortex
Dorsal Column-medial Lemniscus (DCML) pathway?
- Ascending pathway
- Carries sensory information relating to fine touch, conscious proprioception pressure and vibration
- Fine touch, discriminate exactly what and where you are being touched
- Proprioception: Things around you
Pathway/where do the tract neurons go: - First order: Pseudo unipolar sensory neuron ascends in the dorsal column and synapses at the medulla oblongata
- Second order: Interneuron in the medulla oblongata decussates and ascends to synapse in the thalamus
Third order: Interneuron travels from the thalamus to the primary somatosensory cortex
Corticospinal (anterior and lateral) pathway
- Descending pathway
- Anterior tract carries motor information to control skeletal muscles of the trunk and proximal muscles of the limbs
- Lateral tract (90%) carries motor information to control skeletal muscle of the distal limbs.
Proximal: very beginning of the limbs
Pathway/where do the tract neurons go?
Upper motor neuron: Originates in the primary motor cortex and descends to the medulla oblongata
- Anterior corticospinal tract: Neuron continues to descend through the anterior column (white matter) of the spinal cord, where it the decussates and synapses in the ventral horn (grey matter) of the spinal cord
- Lateral corticospinal tract: Decussation occurs in medulla oblongata and neuron continues to descend through the lateral column (biggest white column for motor) (white matter), eventually synapsing in the ventral horn (grey matter) of the spinal cord
Lower motor neuron: Travels from the ventral horn out to the skeletal muscle
Protective features of the CNS:
Axial skeleton:
- Bones of the skull protect the brain
- Shape specifically contoured to the shape of the brain
- Vertebrae protect the spinal cord
Spinal cord sits within the vertebral canal
Meninges?
- Connective tissue (CT) protective coverings of the brain and spinal cord
Three layers:- Dura mater: Outermost layer, tough CT, double layered outer periosteal inner meningeal, has extensions into cranial cavity to limit brain movement
- Arachnoid mater: Middle layer, CT covering, blood vessels and cerebrospinal fluid located deep to arachnoid later in subarachnoid space
Pia mater: innermost layer, delicate CT that clings onto the brain/spinal cord
Cerebrospinal fluid?
- Clear colorless plasma-like fluid that circulates around the brain and spinal cord
- Produced by blood vessels known as the choroid plexus- located in brain ventricles
- Provides mechanical protection of the CNS: buoyancy, shock absorber/liquid cushioning
- Provides nourishment to the CNS: Oxygen/glucose
- Regulates CNS: Exchange of nutrients, removal of wastes, communication
What do parts of the brain do?
- Keeps heart on pace,
- Mid brain: carries out higher level functions, sends out motor responses
- Diencephalon: homeostasis, strong emotions
- Cerebrum: Highest functions, voluntary movements
Fissure separate L R hemisphere
Functions of the cerebral cortex?
- Prefrontal: Executive functions
- Broca’s: Speech production
- Somatosensory cortex: associated with physical feeling, receives information about touch
- Spatial manipulation: Parietal
Occipital: Vision
3 Membranes of the brain?
- Dura mater: protection, attaches brain to skull, blood flow
- Arachnoid mater: less substantial, suspend brain in place
- Subarachnoid space: CFS
- Pia mater: tight membrane, additional barrier, contain CSF, blood vessels held against it before it penetrates the brain
CSF taken out of lumbar cistern: e.g. diagnose meningitis
What are Meninges?
- Connective tissue coverings of the brain and spinal cord: Dura mater, outermost tough/CT
- Double layer - outer periosteal, inner meningeal
- Arachnoid mater: Intermediate/loose CT covering
Pia mater: innermost/delicate CT clings onto the brain
Vertebral column sections?
- Divided into 5 groups, cervical, thoracis, lumbar, sacral, coccyx
- Upper 24 are articulating separated by intercalated discs
- Head - 10-13 pounds
- Cervical: C1-C2 axis to rotate and move head.
- Thoracis: mid/upper back, hold ribcage and protect heart and lungs
- Lumbar: Upper body, larger,
- Sacral: connect spine to hip bones and vertebrae are fused together
- Coccyx: 4 fused bones to provide attachment bones for ligaments and muscles of pelvic floor
- Vertebra: Body, vertebral arch, processes, houses spinal cord, allow for muscle attachment
What are the joints, discs and fluid in the vertebral column?
- Spinal cord is in the vertebra foramen
- Facet joints - each vertebra has two and allow for movement
- Between vertebra are discs which provide cushioning and prevent rubbing
- Discs are composed of annulus which is fibrocartilage to connect the vertebra from above and below
- Nucleus absorbs fluid at night and pressure is pushed down during the day
We shorten as we age because the vertebra discs lose the ability to reabsorb
Anatomy of the spinal cord?
- Location: vertebral canal
- Origin: from foreman magnum of skull
- Termination: L1 and L2 (well short of vertebral canal)
- About 42 cm long and 1.8 cm thick
- Two-way pathway between body and brain
Major reflex center
Spinal cord cross-sectional anatomy:
Grey matter:
- Contains neuron cell bodies
- Shaped like the letter H
- Organized into horns
- Dorsal/posterior - sensory neurons
- Lateral/intermediate - visceral motor
Ventral/anterior - somatic motor neurons
What is a tract or pathway:
- They grey matter of the spinal cord has functional areas e.g. motor neuron cell bodies are found in the ventral horn
- The brain cortex functional areas e.g. primary motor cortex
- Neurons coming from the same place carrying the same type of information to the same part of the brain are located together
This creates a pathway or tract
Spinal cord white matter:
- White matter contains both unmyelinated and myelinated fibers/axon
- White matter links the brain to the spinal and thus the body
- Dorsal column
- Lateral column
- Ventral column
- Each column contains nerve fibers (axon) tracts
- Ascending - sensory tracts/pathways
Descending - motor tracts/pathways
In what two (2) regions of the spinal cord would the spinal nerves supplying Gwendolyn’s (A) arm and, (B) leg be located?
(A) Cervical (B) Lumbar
Which of the following options correctly identifies the (A) neural pathway and, (B) the information carried within the respective pathway that would relate to the statements above?
A) Dorsal Column-Medial Lemniscus pathway (B) Fine touch & pressure
Given what you know about neuronal pathways, which of the neurons in the sensory pathway is most likely to have been directly affected by the stroke?
Third-order neuron
Given what you know about neuronal pathways, which of the neurons in the motor pathway is most likely to have been directly affected by the stroke?
Upper motor neuron
In the event of a haemorrhagic stroke, you would expect the bleed to occur directly between which two meningeal layers?
Arachnoid and Pia Mater
Which of the following options correctly states the (A) Cranial nerve responsible, and (B) The respective function of that nerve, that best explains the symptom outlined in the scenario above?
(A) Oculomotor nerve (B) Motor
