9 - Nervous System Organization Flashcards
What’s the CNS and the PNS?
Central Nervous System (CNS) - brain and spinal cord
Peripheral Nervous System (PNS) - nerve fibres that carry information between the CNS and other parts of the body
What are the three functional classes of neurons?
- Afferent neurons
- Efferent neurons
- Interneurons (found in CNS)
What are the components and function of the CNS?
Components:
- Cerebral cortex
- Cerebellum
- Basal nuclei
- Brain stem
- Hypothalamus
- Thalamus
What protects the CNS?
- Glial cells - 90 % of the cells within CNS, also called neuroglia cells
- Astrocytes - most abundant glial cell and fill a number of critical functions
- Microglia - immune cells of the CNS
- Ependymal - line cavities and contribute to formation of CSF
What is the 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)
What is the role of oxygen and glucose in the brain?
- Brain is highly dependent on constant blood supply, can’t produce ATP in absence of oxygen
- Brain does not store glucose as well
- Damage occurs if oxygen is cut off for ~5 minutes or glucose for > 15 min
What is structure of cerebral cortex?
- Two halves (right and left cerebral hemispheres)
- Thin outer shell of gray matter (densely packaged neuronal cell bodies) on each hemisphere
- Bundles or tracts of myelinated nerve fibres constitute the white matter (transmit signals)
- Corpus callosum allows two hemispheres to communicate
What is plasticity and neurogenesis?
- Ability to change or be functionally remodelled in response to demands placed on it
- When an area of the brain is destroyed, other areas of the brain may gradually assume functions of damaged region
What’s the pathway from sensory input to motor ouput?
- Sensory input
- Primary sensory areas
- Higher sensory areas
- Association areas
- Higher motor areas
- Primary motor cortex
- Motor output
What are the left vs right side of the cerebral hemispheres for?
- Left side is most commonly the dominant hemisphere for fine motor control, so most people are right-handed
- Left side: logica, analytical, sequential, verbal tasks
- Right side: non-language skills, spatial perception, arts, music talents
What is the basal ganglia?
- Consists of several masses of grey matter located deep within the cerebral white matter
- Plays a complex role in movement
What’s the Thalamus?
- Deep in the brain near the basal ganglia
- Serves as a relay station and integration center
What’s the hypothalamus?
- The hypothalamus is an integrating centre that lies beneath the thalamus
- Multifunctional (regulating the internal environment)
What’s the limbic system?
- Limbic system surrounds the brain stem
- Interconnected ring of forebrain structures:
1. Emotion (amygdala)
2. Basic behavioural patterns
3. Reward and punishment centres
What are the three components of the brain stem?
- Pons
- Medulla oblongata
- Midbrain
What are the 5 functions of the brain stem?
- Majority of cranial nerves
- Contains centers that control cardiovascular, respiratiry and digestive function
- Regulates postural muscle reflexes
- Reticular activating system (RAS): controls the overall degree of cortical alertness
- Plays a role in sleep/wake cycle
What is the spinal cord?
Cord that extends from brain stem
Paired spinal nerves emerge from spinal cord through spaces in vertebrae
Thick bundle of elongated nerve roots within the lower vertebral canal is called cauda equina
What are the two neural tissues in spinal cord?
- Spinal cord white matter
- Organizes into tracts (ascending/descending) - Spinal cord grey matter
- Dorsal (posterior) horn
- Ventral (anterior) horn
- Lateral horn
- Located in inner section of the spinal cord
What are 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 same pathway)
What are the 2 divisions of the PNS?
- Afferent division - Sends information from internal and external environment to CNS (carries signals to CNS)
- Efferent division - Communication link by which CNS controls activities of muscles and glands (carries signals from CNS)
What are the two kinds of afferent division?
- Visceral afferent:
Incoming pathway for info from internal viscera (organs in body cavities)
2. Sensory afferent: Somatic sensation (from body surface) Special senses (vision, hearing, taste, smell)
How do receptors work?
- Receptors at peripheral endings of afferent neurons
- Detect stimuli
- Convert forms of energy into electrical signals (APs)
What are 6 types of receptors?
1. Photoreceptors: Responsive to visible wavelengths of light 2. Mechanoreceptors: Sensitive to mechanical energy 3. Thermoreceptors: Sensitive to heat and cold 4. Osmoreceptors Detect changes in conc. of solutes in body fluids 5. Chemoreceptors: Sensitive to specific chemicals 6. Nociceptors - Pain receptors that are sensitive to tissue damage or distortion of tissue
What effect does stimulus have on receptor’s permeability?
- Stimulus alters permeability, which leads to graded receptor potential
- Usually causes nonselective opening of all small ion channels
- this change in membrane permeability can lead to the influx of sodium ions (Na+) - produces receptor potentials
- The magnitude of the receptor potential represents the intensity of the stimulus - a receptor potential of sufficient mag can produce an AP (AP propagated along afferent fibre to the CNS)
(receptors are either specialized ending of an afferent neuron or the separate cell closely associated with peripheral ending of a neuron)
