Neurology #1 Flashcards
Parts of Nervous System
3 Parts:
1.) Central Nervous System (CNS)
2.) Peripheral Nervous System (PNS)
3.) Enteric Nervous System (ENS)
- PNS functions as input-output system for relaying information to the CNS and for transmitting output messages that control effector organs, such as muscles and glands.
Central Nervous System (CNS)
- Consists of brain & spinal cord
- Protected by skull & vertebral cortex
Peripheral Nervous System (PNS)
Nervous tissue outside of the CNS & ENS
- Functionally divided into 2 parts:
1.) Afferent Division
- Delivers sensory information from special sensory receptors, visceral sensory receptors, & somatic sensory receptors to the CNS
- CNS then integrates, processes, and coordinates sensory input and motor commands and carries commands to efferent division
2.) Efferent Division
- Divided into Somatic Nervous System (SNS) and Autonomic Nervous System (ANS)
Somatic Nervous System (SNS)
- Part of PNS
- Controls muscle contraction at conscious and sub-conscious level
Autonomic Nervous System (ANS)
Part of PNS:
- Regulates: smooth muscle, cardiac muscle, glandular secretions, & adipose tissue
- Usually occurs at sub-conscious level
Further divided into:
- Parasympathetic Division (rest + digest)
- Sympathetic Division (flight + flight)
Enteric Nervous System (ENS)
- Network of neurons and nerves found in walls of the digestive tract
3 Sensory Receptor Types
Special sensory receptors:
- monitor smell, taste, vision, balance, and hearing
Visceral sensory receptors:
- monitor internal organs
Somatic sensory receptors:
- monitor skeletal muscles, joints, and skin surface
Major Cell Types of Nervous System
1.) Neurons
- Functioning cells of the nervous system
2.) Glial Cells
- Protect the nervous system and supply metabolic support
Neurons
Functioning cells of nervous system:
- Exhibit membrane excitability and conductivity and secrete neurotransmitters and hormones (e.g, epinephrine)
- Have ability to communicate with other neurons and body cells through electrical impulses or action potentials.
Consist of: cell body w/ cytoplasm filled processes, the dendrites and the axons
2 types of neurons:
1.) Afferent Neurons (Sensory Neurons)
- carry information to the CNS
2.) Efferent Neurons (Motor Neurons)
- carry information from the CNS to the effector organs
Interconnecting Neurons
- Between afferent and efferent neurons
- AKA Interneurons or Internuncial neurons
- Modulate and control the body’s response to sensory input from internal and external environments.
Metabolic Requirements for Nervous Tissue
Brain = 2% of body weight
- Receives 15% of resting cardiac output
- Consumes 20% of CO oxygen
Brain does not:
- Store oxygen or engage in anaerobic metabolism
- Store nutrition (e.g, glycogen, glucose)
- Recover nervous tissue injury (e.g, no centrioles)
Brain survival:
- Without oxygen = 10 seconds
- Death of brain cells (apoptosis) = 4-6 minutes
Fuel Source for Nervous System
Glucose:
- Major fuel source
- Neurons have no provision for storing glucose
Ketones:
- Can provide for limited temporary energy requirements
- Rapidly depleted
- Neurons have no glycogen stores and rely on glucose from the blood or glycogen stores of supporting neuroglial cells
Action Potentials
Rapid sequence of changes in the voltage across a membrane:
- Temporary shift (from negative to positive) in the neuron’s membrane potential caused by ions suddenly flowing in and out of neruron.
- Occurs when a neuron sends information down an axon and away from cell body.
4 Steps:
1.) Resting Potential - Sodium (Na+) and potassium (K+) channels are closed.
2.) Depolarization - Na+ channels open in response to stimulus.
3.) Repolarization - Na+ channels close and K+ channels open.
4.) Resting Conditions - Na+ and K+ channels are closed.
All of none principle (Threshold potential = 55 mV)
Structures of Brain
4 Major Brain Regions:
1.) Cerebrum
2.) Cerebellum
3.) Diencephalon
4.) Brain Stem
Cerebrum
- Largest part of human brain
- Separated into 2 half’s:
1.) Left Cerebral Hemisphere
2.) Right Cerebral Hemisphere
4 Regions:
1.) Frontal lobe
2.) Parietal lobe
3.) Occipital lobe
4.) Temporal lobe
- Cerebral Cortex : outer layer that covers surface of cerebrum
- Gyrus (gyri) : rounded elevations that increase surface area
- Sulcus (sulci) : shallow grooves that separate gyri and brain regions
- Longitudinal Fissure : separate right side from left side
- Central Sulcus : divides brain from front to back
- Precentral Gyrus (primary motor cortex) : somatic muscle control
- Postcentral Gyrus (primary sensory cortex) : processing of sensory information
Functions:
- Regulates temperature
- Conscious thought processes
- Intellectual functions (speech, judgement, thinking & reasoning, problem solving, emotions, and learning)
- Memory storage and processing
- Initiates and coordinates movement (conscious and subconscious regulation of skeletal muscle contractions)
Parietal Lobe
- Sensory function
- Processes information received from outside world such as touch, taste, and temperature.
Includes:
- Primary sensory cortex (postcentral gyrus)
- Somatic sensory association area
Frontal Lobe
- Motor function
- Important for voluntary movement, expressive language, and managing higher level executive functions
- Most common region of injury in traumatic brain injury
Includes:
- Primary motor cortex (precentral gyrus)
- Somatic motor association cortex (premotor cortex)
Occipital Lobe
- Visual perception, including colour, form and motion
Includes:
- Visual cortex
- Visual association area
Temporal Lobe
- Hearing
- Processing auditory information
Includes:
- Auditory association area
- Auditory cortex
Wernicke’s Area
- Language comprehension (ability to understand language)
- Supports component of speech production (phonologic retrieval)
- Communicates with sensory cortex and its association areas
Broca’s Area
- Motor speech area
- Movement nesacarry to speak
- Communicates with motor cortex and association areas
- Located in inferior frontal gyrus
Basal Nuclei
- Group of subcortical structures (gray matter) found deep within the white white matter of the brain.
- Subconsciously control skeletal muscle tone and lung movements.
- Activity regulated (inhibited) by dopamine which is secreted by substantia nigra.
- If substantia nigra is damaged, less dopamine will be secreted.
- Less dopamine = less inhibition of activity for basal nuclei resulting in overactivity: (uncontrolled movements, rigidity, tremors)
- Parkinson’s Disease
Cerebellum
- Second largest part of brain
- Posterior to Cerebrum
- Balance and coordination of movements
- Sensitive and responsive to toxins in brain (alcohol intoxication causes dizziness and loss of balance)
Diencephalon
Three regions:
1.) Hypothalamus
- Lies at floor of Diencephalon
- Involved in controlling emotions, autonomic functions, and hormone production
- Exempted from the blood brain barrier (BBB,) can freely access cerebral spinal fluid and interstitial fluid
- Link between nervous system and endocrine system
2.) Thalamus
- Contains relaying and processing centres for sensory information
- All information from body’s senses (except smell) must be processed through thalamus before being sent to brain’s cerebral cortex for interpretation
3.) Epithalamus
- Connects limbic system to other parts of the brain
- Contains pineal gland (secretes melatonin)
Brain Stem
3 Structures:
1.) Midbrain
- Involved in processing auditory and visual information
- Controls reflexes in response to stimuli
- Maintains consciousness and alertness
2.) Pons
- Relays sensory information to cerebellum and thalamus
- Contain nuclei which are responsible for somatic and visceral motor control
3.) Medulla oblongata
- Connects the brain to the spinal cord
- Relays sensory information to the thalamus and other regions of the brain stem
- Centre for regulating autonomic activities (HR, BP, RR, & digestion)
Brain Protection
Cranial Bones
Blood Brain Barrier
Cerebral Spinal Fluid
Cranial Meninges
- Supportive membrane with 3 layers:
1.) Dura Mater (Outer)
2.) Arachnoid Mater
3.) Pia Mater (Inner)
- No epidural space
- No subdural space (except in trauma or illness)
Subarachnoid Space
- Between arachnoid mater and pia mater
- Contains cerebral spinal fluid
Cerebral Spinal Fluid (CSF)
- Surrounds exposed surfaces of Central Nervous System
- Synthesized in ventricles of brain (3rd & 4th)
- Supports the brain
- Cushions the brain and spinal cord against physical trauma
- Transports nutrients, chemical messengers, and wastes
Ventricular System of Brain
4 Ventricles:
1, 2.) x2 Lateral Ventricles
- Each cerebral hemisphere consists of a lateral ventricle
- Do not directly communicate with each other, but communicate with Third Ventricle
- Communication occurs via inter-ventricular foramen
3.) Third Ventricle
- Located in Diencephalon
4.) Fourth Ventricle
- Located within posterior surface of pons, anterior surface of cerebellum, and superior medulla of oblongata region.
- Narrows and joins central canal of spinal cord
Third & Fourth Ventricle communicate with each other via cerebral aqueduct
Production of CSF
- Each ventricle contains Choroid Plexus which are responsible for synthesis of CSF
- Specialized ependymal cells are connected via tight junction and surround choroid plexus capillaries
- CFS produced as filtrate when fluid leaks out of capillaries in choroid plexuses
- Ependymal cells then secrete CSF into ventricles
Circulation of CSF
Reticular Activating System
- Network of neurons located throughout brainstem
- Neurons make up complex set of networks in the core of brainstem that extend from the upper part of the midbrain to the lower part of the medulla oblongata
Functions:
- Somatic motor control
- Cardiovascular control
- Pain modulation
- Sleep and consciousness
Level of Consciousness (LOC)
- Reflect awareness of and response to environment
- Assessed by Glasgow Coma Scale
Brain Death
Irreversible loss of function of the brain, including the brain stem
- e.g., no motor response; apnea; no brainstem reflexes: ( gag, cough, doll’s eyes (oculocephalic))
Must meet developed criteria:
1.) Irreversible brain death with established etiology capable of causing neurologic death
2.) Deep, unresponsive coma with absent motor responses, excluding spinal reflexes
3.) Absent brain stem reflexes (gag, cough) and absence of corneal responses, pupillary responses with pupils at mid-size or greater and vestibulo-ocular response
4.) Absent respiratory effort based on apnea test (disconnection of the ventilator after pre-oxygenation, and observation for spontaneous breathing)
5.) Absent confounding factors (e.g., unresuscitated shock, hypothermia, drug intoxications, neuromuscular blockade).
Global Ischemia
Occurs when blood flow is inadequate to meet the metabolic needs of the entire brain
- unconsciousness occurs within seconds resulting from complete cessation of blood flow (cardiac arrest) or from marked decrease in blood flow (cardiac arrhythmias)
Compounding issues:
- cerebral edema
- watershed infarcts = heightened focal damage to lowered-flow regions (e.g., hippocampus)
- reperfusion of injured tissues = secondary injury due to belated reperfusion, caused by inflammatory mediators, toxic byproducts, catecholamines, or nitric oxide (reperfusion injury compounds original injury)
- electrolyte imbalances (Na, K, Ca)
e.g. electrolyte dysfunction: excess intracellular calcium = calcium cascade: protein breakdown, DNA injury, free radical formation, lipid peroxidation, mitochondrial injury = cell death
