nervous system pt 1

• What are reigons of the brain?

  • Cerebral hemisphere
  • Diencephalon
  • Cerebellum
  • Brain stem - midbrain, pons, medulla obongata

  
• Brain organisation: what is in grey matter and white matter?

  Grey matter:

  • Neuronal cell bodies
  • short, non myelinated axons
  • Axon terminals
  • Dendrites
  • Synapses
  • glial cells

  White matter:

  • mostly myelinated axons
  • some non myelinated axons
  • glial cells
• Distribution pattern of grey & white matter in CNS

  1. The spinal cord basic pattern: a central cavity surrounded by grey matter, with outer white matter
  2. The brain stem has additional regions of grey matter (brain nuceli) buried within the white matter
  3. The Cerebrum and cerebellum have isalnds of grey matter (nuclei) within white matter, as well as an outer cortex of grey matter

  
• Ventricles

  • Lateral ventricle
  • Third ventricle
  • cerebral aqueduct
  • Fourth ventricle

  
• Lobes, sulci & fissures of cerebrum

  • Longitudinal fissure - deep groove that seperates two cerebral hemispheres of the vertebrate brain

  
• Cerebral hemisphere

  three basic regions:

  • Cerebral cortex of grey matter superficially
  • White matter internally
  • Basal nuclei deep within matter

  
• Cerebral cortex

  • 'Executive suite’ of brain
  • Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding
  • Thin superficial layer of grey matter
  • Composed of neuron cell bodies, dendrites, axon terminals, synapses, glial cells, blood vessels, nonmyelinated axons
  • 40% of mass of brain
• Cerebral cortex

  Contains three types of functional areas:

  • Motor areas: control voluntary movement
  • Sensory areas: conscious awareness of sensation
  • Association areas: integrate diverse information

  Each hemisphere is concerned with contralateral (opposite) side of body

  Conscious behaviors involve entire cortex in various ways
• Cerebral cortex- Motor areas

  Primary (somatic) motor cortex

  • Located in precentral gyrus of frontal lobe
  • Pyramidal cells: large neurons that allow conscious control of precise, skilled, skeletal muscle movements
  • Pyramidal tracts: formed from long axons of pyramidal cells project down spinal cord (corticospinal) or brain stem (corticobulbar tract)
  • Somatotopy: all muscles of body can be mapped to area on primary motor cortex
  • Motor homunculus: upside-down caricatures represent contralateral motor innervation of body region
• Cerebral cortex - Motor areas

  Broca’s area

  • Present in one hemisphere (usually the left)
  • Motor speech area that directs muscles of speech production
  • Active in planning speech and voluntary motor activities

  Frontal eye field

  • Controls voluntary eye movements
• Clinical correlation - primary motor cortex

  • Damage to areas of primary motor cortex, as seen in a stroke, paralyses muscles controlled by those areas
  • Paralysis occurs on opposite side of body from damage
• Clincal correlation- Premotor area

  • Damage to premotor area controlling movement of fingers would still allow fingers to move, but voluntary control needed to type would be lost
  • Other premotor neurons can be reprogrammed to take over skill of damaged neurons (Would require practice)
• Cerebral cortex - sensory areas

  • Occur in parietal, insular, temporal, and occipital lobes

  8 main areas include:

  • primary somatosensory cortex
  • visual areas
  • auditory areas
  • olfactory cortex
  • gustatory cortex
  • visceral sensory area (insular cortex)
  • somatosensory association cortex
  • vestibular cortex (location not well defined, right hemisphere dominance?)
• Cerebral cortex - sensory (primary somatosensory cortex)

  • Location: postcentral gyrus of parietal lobe
  • Receives general sensory information from skin and proprioceptors of skeletal muscle, joints, and tendons
  • Capable of spatial discrimination: identification of body region being stimulated
  • Somatosensory homunculus: upside-down caricatures represent contralateral sensory input from body regions
• Cerebral cortex- sensory (somatosensory association cortex)

  • Posterior to primary somatosensory cortex
  • Integrates sensory input from primary somatosensory cortex for understanding of object
  • Determines size, texture, and relationship of parts of objects being felt
• Clinical correlation- Primary visual cortex

  • Damage to the primary visual cortex results in functional blindness
  • By contrast, individuals with a damaged visual association area can see, but they do not comprehend what they are looking at, visual agnosia
• cerebral cortex - Multimodal association areas

  • Receive inputs from multiple sensory areas
  • Send outputs to multiple areas
  • Allows us to give meaning to information received, store in memory, tie to previous experience, and decide on actions
  • Sensations, thoughts, emotions become conscious: makes us who we are
  • Broadly divided into three parts: anterior, posterior, and limbic association area
• Cerebral cortex- MAA (anterior association area)

  • Also called prefrontal cortex
  • Most complicated cortical region
  • Involved with intellect, cognition, recall, and personality
  • Contains working memory needed for abstract ideas, judgment, reasoning, persistence, and planning
  • Development depends on feedback from social environment
• Cerebral cortex- MAA (posterior association area)

  • Large region in temporal, parietal, and occipital lobes
  • Plays role in recognising patterns and faces and localising us in space
  • Involved in understanding written and spoken language (Wernicke’s area, > 90% people in left cerebral hemisphere)
• Cerebral cortex - MAA (Limbic association area)

  • Part of limbic system
  • Involves cingulate gyrus, parahippocampal gyrus, and hippocampus
  • Provides emotional association with an event and helps establish memories
• Cinical association area- anterior association area

  • Tumors or other lesions of the anterior association area (i.e. prefrontal cortex) may cause mental and personality disorders, including loss of judgment, attentiveness, and inhibitions
  • Affected individual may be oblivious to social restraints, perhaps becoming careless about personal appearance, or take risks
• Clincial correlation- posterior area

  • Individuals with lesions in the part of the posterior association area may have problems with self awareness in space
  • Individual may refuse to wash or dress the side of the body opposite to lesion because “that doesn’t belong to me”
• Lateralisation of cortical functioning

  Lateralisation: tendency for some cortical functional or processes to be specialized to one hemisphere 

  • Hemisphere are not identical; unique lateralization in individual
  • Allows diff function being carried out simultaneously pn 2 hemispheres to increase cognitive capacity 

  Cerebral dominance: Hemisphere that is dominant for cerebral functions 

  • Handedness 
  • 90% of humans are right handed 
  • 1% are ambidextrous - user either hand 
  • 25% genetics factor factors, 75% environmental factors 

  Language 

  • Vast majority of right handers- left hemisphere dominance
• Lateralisation of Cortical functioning 

  Left hemisphere 

  • Broca’s and Wernicke’s areas (controls language), exact calculation and fact retrieval (linked to lang centre)

  Bilateral

  • Info processing in the sensory cortices is essentially identical 
  • Hemispheres communicate almost instantaneously via fibre tracts and functional integration
• Cerebral white matter

  Second of three basic regions of cerebral hemispheres 

  • Responsible for communication between diff area of grey matter within CNS; within cortex, and between cortex and lower CNS 
  • Consists of myelinated fibres bundles into large tracts 
  • Classified according to direction they run: 
  • Association, commissural & projection fibres
• Cerebral fibre tracts

  Corpus callosum- largest set of commissural fibres in brain - important pathway for speech-lang functions 

  Corona radiata- most prominent projection fibres - radiate out from the cortex and then come together in brain stem. Projection fibres that make up the corona radiata also radiate out of the brainstem via the internal capsule 

  
• Cerebral fibre tracts

  Association fibres

  Commissural fibres - corpus callosum

  Projection fibres- corona radiata, internal capsule

  
• Basal Nuclei (Ganglia)

  Main components of basal ganglia- 

  • Stranium (both dorsal striatum (caudate nucleus and putamen) and ventral striatum (nucleus accumbens & olfactory tubercle))
  • Globus pallidus
  • Ventral pallidum 
  • Substantia nigra 
  • Subthalamic nucleus

  
• Basal nuclei (Ganglia) Motor functions

  • Voluntary movements are not initiated here (in the cortex)
  • Influence muscle movements
  • Regulate intensity of slow or stereotyped movements
  • Filter out incorrect/inappropriate responses
  • Inhibit antagonistic /unnecessary movements
• Basal nuceli (Ganglia) Cognitive functions

  • Selecting & enabling various cognitive,executive or emotional programmes store in other cortical areas
  • Implicit learning and memory (e.g cycling, swimming)
• Disorders of the basal nuclei

  Parkinson's disease: Death of dopaminergic neurons in substantia nigra

  
  

  Huntington's disease: death of neurons in striatum
• Diencephalon

  consists of three paired grey matter structures:

  • Thalamus
  • Hypothalamus
  • Epithalamus
• Thalamus

  • Bilateral egg-shaped nuclei- forms superolateral walls of third ventricle 
  • 80% of diencephalon 
  • Bilateral nuclei connected by interthalamic adhesion 

   -contains several nuclei, named for location 

  Each nucleus projects (directly) to and receives fibres (indirectly) from cerebral cortex, and has a functional speciality

  
• Thalamus


  Relay sensory & motor signals from subcortical areas to cerebral cortex (except for olfactory cortex- olfactory bulb); gateway to the cerebral cortex
• Function of thalamus


  1. Sorts, edits and relays ascending input

  2. Impulses form hypothalamus for regulating emotion and visceral function

  3. Impulses from cerebellum and basal nuclei to primary cortex and coordinate voluntary movement

  4. Impulses from inferior colliculus in midbrain relaying auditory information

  5. Impulses for learning and memory

  6. Impulses for memory or sensory integration
• Function of Thalmaus

  Reciprocal connections with cerebral cortex

  - Regulate states of sleep and wakefulness

  - Consciousness, cortical arousal
• Hypothalamus

  • located below thalamus
  • Forms cap over brain stem and form inferolateral walls of third ventricle 
  • Contains many important nuclei such as: 
  • Mammillary bodies: paired anterior nuclei, imp for recollective memory 
  • Infundibulum:stalk that connects to pituitary gland
• Hypothalamus


  Main visceral control and regulating centre that is vital to homeostasis
• Functions of hypothalamus

  Initiated physical responses to emotions

  - Part of limbic system: percieves pleasure, fear, rage,biological rhythms, drives (sex drive)

  • Regulates body temperature: sweating or shivering
  • Regulates hunger and satiety:response to nutrient blood levels or hormones
  • Regulates water balance and thirst
  • Regulates sleep-wake cycles
  • Controls endocrine system functions - secretions of anterior pituitary gland, production of posterior pituitary hormones
• Function of Hypothalamus Controls

  
  

  Autonomic nervous system

  1. Blood pressure

  2. Rate and force of heartbeat

  3. Digestive tract motility

  4. Pupil size