W1 - Cells of the NS, Cerebral Cortex and White Matter

Composition of the Brain

• R/L Cerebral Hemispheres (Cerebrum)

• Diencephalon

• Brainstem

• Cerebellum

Cerebrum Composition

• Cerebral Cortex = outer crust of cerebral gray matter, location of conscious mind

• Cerebral White Matter = neuron fiber tracts deep to the cerebral cortex

• Basal Nuclei (Basal Ganglia) = islands of gray matter buried within the white matter

• Limbic System = gray and white matter structures dispersed thruout the cerebrum

Gross Anatomical Features of the Brain

• gyri = folds that increase SA, numerous

• sulci = shallow grooves between the gyri

• fissure = deep grooves that sep larger portions of the cerebrum

Lobes of the Cerebral Hemisphere

• frontal

• parietal

• occipital

• temporal

Frontal Lobe

contains primary motor cortex- voluntary control of skeletal muscles

Parietal Lobe

contains primary somatosensory cortex- conscious perception of touch, pressure, pain, vibration, temp

Occipital Lobe

contains visual cortex- conscious perception of visual stimuli

Temporal Lobe

contains auditory cortex and olfactory cortex- conscious perception of auditory and olfactory stimuli

Fissures of the Brain (Sylvian fissure = Lateral Fissure/Sulcus)

Insula

located deep within the lateral fissure- involved in sensory processing, emotions and self awareness

Hemispheric Functionality

while both hems are involved in most functions, they are specialized

• LT = language, numerical and scientific skills

• RT = complex visual-spatial skills, communicate emotional significance to events and language, music perception

Pre/Post- Central Gyrus aka

primary motor/sensory cortex 

A lesion in the Somatosensory Area

causes contralateral loss of sensations, can perceive sensation but cannot tell the degree or origin

A lesion in the Primary Motor Area

contralateral paralysis

Special Sense Areas of the Cerebral Cortex

• Insula = Gustatory (taste)

• Occipital = Visual

• Temporal = Olfactory, Auditory

Special Cerebral Cortex Areas for Speech and Language

• Broca’s Area = speech muscles

• Wernicke’s Area = permits recognition of spoken and written language, create plan of speech

Types of Tracts within Cerebral White Matter

• association = confined to the same hem

• commissural = run between R/L hems

• projection = project to and from the cerebral cortex and form asc/desc tracts

Corpus Callosum

• important white matter commissural tract

• components: rostrum, genu, body, splenium

Four Main Tissues

• nervous

• muscle

• epithelial

• connective

cells of the NS

• neurons

• neuroglia

neurons vs. neuroglia

neurons:

• electrically excitable (AP)

• cellular structures

• cannot divide

neuroglia

• not electrically excitable

• supporting structures

• can divide/multiply 

layout of the NS

• CNS

  • brain

  • spinal cord

• PNS (Peripheral NS)

  • cranial nerves

  • spinal/peripheral nerves

  • nerve plexuses

PNS

• extension from the CNS

• consists of all the nervous tissue outside of the CNS

Functions of the NS

• sensory = detect changes thru sensory receptors

• integrative = analyze sensory info, store info, make decisions

• motor = respond to stimuli via effectors

PNS Function

acts as a communication line between

• sensory receptors → CNS

• CNS → effectors (glands, muscles)

Cranial and Spinal Nerves consist of

• afferent neurons = sensory information from the periphery to the CNS

• efferent neurons = motor information from the CNS to the periphery

Functional Divisions of the PNS

• Somatic NS

• Autonomic NS

• Enteric NS

Flow of the NS

Sensory Components of the PNS (sensory receptors and neurons of the SNS, ANS, ENS) → CNS → Motor Components of the PNS (motor neurons) → Effectors (muscles, glands)

Sensory Components of the PNS (Afferent)

• somatic sensory neurons

• visceral sensory neurons

Somatic Sensory Neurons

carry sensory info that one is conscious of

• temp

• pain

• touch

• proprioception (sense of own movement/position in space)

• muscle stretch

• special senses

Visceral Sensory Neurons

carry sensory information that one is not conscious of

• BP

• blood gases

• distension

• change in pH

Motor Components of the PNS (Efferent)

• Somatic Motor Neurons

• Autonomic Motor Neurons

Somatic Motor Neurons

voluntary actions- conscious control of skeletal muscle contraction

Autonomic Motor Neurons

involuntary actions- unconscious control of smooth/cardiac muscles, gland secretions

ANS Subdivisions

• sympathetic (fight or flight)

• parasympathetic (rest and digest)

Functional Classification of Neurons

classified based on the direction of the AP propagation

• afferent: to the CNS

• efferent: from the CNS

• interneurons/association (the CNS): process sensory info and elicit motor response

Cell Bodies of the Neuron Terminology

• PNS

• CNS

• PNS = ganglia/ganglion

• CNS = nuclei/nucleus

Components of the Neuron - Dendrites

multiple short and branches procesess off the cell body that receives input from neighboring neurons via neurual synapse

Components of the Neuron - Axon

• single long cellular process that is connected to the cell body at the axon hilock

• AP initiated at the initial segment → transmitted along the axon towards a another neuron/muscle fiber/gland cell

Components of the Neuron - Axon Terminals

• division of axons

• synaptic end bulbs contain synaptic vesicles that store neurotransmitters (molecules that excite or inhibit other neurons/muscle fibers/gland cells)

Presynaptic vs. Postsynaptic Neurons

the presynaptic neuron signals to the dendrites of the postsynaptic neuron at the neurual synapse

Axons of Neurons Terminology

• PNS

• CNS

• PNS = nerves

• CNS = tracts

Neuroglia in the CNS

• astrocytes = strength/support, blood-brain barrier

• microglia = phagocytes

• ependymal cells = production of CSF

• oligodendrocytes = myelination of axons of CNS neurons

Neuroglia in the PNS

• satellite cells = regulate extracellular environment of PNS neurons (like astrocytes in CNS)

• schwann cells = myelination of axons of PNS neurons

Myelination

• a process which a fatty protein layer, called myelin sheath, forms around axons

• provides electrical insulation of the axons, increases speed of AP conduction

Nodes of Ranvier

gaps in myelin sheath along the axon

Two Types of Neuroglia that produce Myeline sheaths

• oligodendrocytes (CNS)

• Schwann cells (PNS)

Gray vs. White Matter

• gray = regions with many cell bodies and dendrites

• white = regions with many axons