9. Nervous System Organisation Flashcards
CNS is..
Central Nervous System - brain and spinal cord
PNS is..
Peripheral Nervous system - nerve fibres that carry information between the CNS and other parts of the body
Afferent vs. Efferent
Afferent - inwards towards CNS
Efferent - e.g. motor command
Sensory vs. Visceral stimuli
Related to Afferent division
Sensory - touch, see, smell etc
Visceral - input from organ sensors
Efferent Division
- splits into somatic and autonomic nervous system
somatic: Voluntary motor movement e.g. move my arms, skeletal muscles (aware/conscious)
autonomic: sympathetic and parasympathetic nervous system, rest of muscle types (not consciously controlling)
What is this
CNS and PNS overview
3 functional classes of neurons
- afferent neuron - starts in PNS, end in CNS
- efferent neuron - start in CNS, end in PNS
- interneurons - starts and end in CNS - (can connect afferent neuron and efferent neurons and interneurons mainly found in brain)
Structure and function of CNS
Brain and spinal cord
cognition referee to the act or process of ‘knowing’ including awareness and judgement
no part of the brain works in isolation
Brain diagram
Core vital life functions in centre of brain
Thought processes and thinking in cerebral or outer brain layer
Major brain functions
Protection of the CNS
Glial Cells - support cells (90% if cells within CNS, called neuroglia cells)
- don’t conduct nerve impulses
Astrocytes - most abundant glial cell and fills a number of critical functions
Microglia - immune cells of the CNS
Ependymal - line cavities and contribute formation of CSF (cerebral spinal fluid)
Protection of CNS diagram
Note oligodendrocyte are…
Blood brain barrier
- Shields brain from harmful changes in the blood
- Consists of endothelial cells
- Tight junctions prevent exchange across the capillary wall
- Lipid soluble substances such as oxygen and alcohol can penetrate cells
- ie if not lipid soluble needs a carrier protein
Role of Oxygen and Glucose
- Brain is highly dependent on constant blood supply
- Brain can not produce ATP in absence of oxygen
- Brain does not store glucose
- Damage occurs if oxygen is cut off for 5 mins or glucose for more than 15 mins
Cerebral Cortex
- largest portion of the brain
- Two halves (right and left cerebral hemispheres joined by corpus callosum)
- Corpus callosum allows two hemispheres to communicate and cooperate with each other
Brain picture
2 halves
note: corpus callosum is in middle
Cerebal Cortex colour
- Thin outer shell of grey matter (neuronal cell bodies) on each hemisphere - densely packaged
- Bundles or tracts of myelinated nerve fibres (axons) constitute the white matter - Transmit signals from one part of the cerebral cortex to another and to other regions of the CNS
Outer brain diagram
Motor Homunculus
(and left side brain, left side body)
Plasticity and Neurogenesis
- ability to change or be functionally remodelled in response to the demands
- when an area of the brain is destroyed other areas of the brain may gradually assume some or all of the functions of the damaged region
Sensory Input to Motor output example
- going from low level/sensitivity data to higher level choices in brain
Cerebral Hemispheres
left side is commonly dominant hemisphere for fine motor control, so most people are right handed
left side excels in logical, analytic, sequential & verbal tasks
right side excels in nonlanguage skills such as spatial perception, arts & music
Basal Ganglia
consist of several masses of grey matter located deep within the cerebral white matter
– Complex role in movement
Thalamus
deep in brain near the basal ganglia
- serves as a relay station and integrating centre
Hypothalamus
is an integrating centre that lies beneath the thalamus
- multifunctional regulating the internal environment
Limbic System
surrounds brain stem and not a separate structure
an interconnected ring of forebrain structures
related to
- emotions - amygdala
- basic behavioural patterns
- reward and punishment centres
Brain stem
- pons
- medulla oblongata
- midbrain
5 functions of the brain stem
Five Functions of the Brain Stem
Majority of cranial nerves arise from the brain stem
Contains centers that control cardiovascular, respiratory, and digestive function
Regulates postural muscle reflexes
Reticular activating system (RAS): controls the
overall degree of cortical alertness
Plays a role in the sleep–wake cycle
Spinal cord
- spinal cord extends from brain stem
- paired spinal nerves emerge from the spinal cord through spaces in vertebrae
- thick bundle of elongate nerve roots within the lower vertebral canal is called the caudal equina - like a horse’s tail
Organization of Neural Tissue in the Spinal Cord
opposite in spinal cord
Spinal Cord White Matter
– Organised into tracts (ascending and descending tracts)
– Located in the outer section of the spinal cord
Spinal Cord Grey Matter
- Dorsal (posterior) horn - receiving sensory input (afferent neurons)
- Ventral (anterior) horn - motor input (with efferent neurons)
- Lateral horn - autonomic processes
- Located in inner section of the spinal cord
Spinal Nerves
- Spinal nerves connect with each side of the spinal cord by a dorsal root and a ventral root
- A spinal nerve consists of both afferent and efferent fibres
- A nerve is a bundle of peripheral neuronal axons enclosed by a connective tissue covering and following the same pathway
- the arms will be higher on the spine compared to the legs for example
Levels in the spinal cord
- cervical nerves - neck
- thoracic nerves - upper body
- lumbar nerves - lower back, pelvis, legs
- sacral - urinary tract
- coccygeal nerve
The PNS (Peripheral Nervous System)
The PNS consists of nerve fibres that carry information between the CNS and other parts of the body
Afferent division of the PNS: Sends information from internal and external environment to CNS (i.e. carries signals to CNS).
Efferent division of the PNS: Communication link by which CNS controls activities of muscles and glands (i.e. carries signals from CNS).
- Nerve, bundle of nerve fibres, called fascicles bundles with other fascicles and connective tissue
- As it moves further from spinal cord it branches off and splits into single nerves
Afferent Division - towards central nervous system
-
Visceral afferent
- Incoming pathway for information from internal viscera (organs in body cavities)
-
Sensory afferent
- somatic (body sense) sensation - arising from body surface and proprioception and where you are in space/touch
- Special senses - vision, hearing, taste, smell
Receptor Physiology
Structures (receptors) at peripheral endings of afferent neurons
Detect stimuli (change detectable by the body e.g. temperature)
Convert forms of energy into electrical signals (action potentials)
– Process is called transduction
Types of Receptors
Photoreceptors - responsive to visible wavelengths of light
Mechanoreceptors - sensitive to mechanical energy (pressure, stretch, vibration)
Thermoreceptors - sensitive to temp/hot & cold
Osmoreceptors - detect changes in concentration of solutes in body fluid and resultant changes in osmotic activity
Chemoreceptors - sensitive to specific chemicals, & include receptors for smell and taste and receptors that detect O2 and CO2 concentrations in blood and chemical content of digestive tract
Stimuli and Receptor Permeability
Receptors may be either
– The specialized ending of an afferent neuron
– a separate cell closely associated with peripheral ending of a neuron
- • Stimulus alters receptor’s permeability, which leads to graded receptor potential > then reach a threshold and cause an action potential
- nonselective opening of all small ion channels – This change in membrane permeability can lead to the influx of sodium ions
- This produces receptor (generator) potentials
The magnitude of the receptor potential represents the intensity of the stimulus - a receptor potential of sufficient magnitude can produce an action potential.
This action potential is propagated along an afferent fibre to the CNS
Types of receptors and speed of adaptation
- receptors may adapt slowly or rapidly to sustained stimulation
- tonic receptor - do not adapt or slowly e.g. muscle stretch receptors, joint proprioceptors
- phasic receptor - rapidly adapting e.g. tactile receptors in skin
Efferent Division
Autonomic nervous system (ANS)
– Involuntary branch of PNS
– Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue
Somatic nervous system
– Subject to voluntary control
– Innervates skeletal muscle
Autonomic Nervous System
- sympathetic nervous system - fight or flight, emergency or stress
- promotes responses that prepare body for physical activity
- parasympathetic nervous system – quiet and relaxed situations
- promotes body-maintence activities such as digestion
Effects of autonomic nervous system on various organs
Somatic Nervous system
Consists of axons of motor neurons from spinal cord or brain stem and end on skeletal muscle
Motor neurons are the final common pathway by which various regions of CNS exert control over skeletal muscle activity - areas of CNS include spinal cord, motor regions of cortex, basal nuclei, cerebellum, and brain stem
