3: The Central Nervous System Flashcards
Integration of the Spinal Reflexes
Sensory information comes in via the sensory neurons through the dorsal root. Interneuron integrates the information and a motor response exits through the ventral roots via the motor neurons.
Spinal Cord: Crude Touch, Temperature and Pain
- CTP: crude touch, temperature and pain
- Spinothalamic tract takes sensory information regarding CTP up to the thalamus so the thalamus can send info to the important areas
- Crosses at the level at which it enters
Spinal Cord: Touch and Proprioception
- Dorsal column
- Information ascends immediately and doesn’t cross until it gets up to a much higher level around the level of the brain stem
Spinal Cord: Voluntary Movement
- Corticospinal tract: from cortico to spine
- Motor message
- Crosses over quite high near brain stem, descends and enters the corticospinal tract, exits via the ventral root
Venous Drainage from the Brain
- All the blood taken up to the brain is drained via the venous system
- Exits via the jugular vein on the way to the heart once it has been deoxygenated in the brain
Protection of the Brain’s Blood Supply: Centrally
The brain always gets a constant supply of blood except for when cardiac output can’t handle it or when there’s a rise in inter cranial pressure.
Protection of the Brain’s Blood Supply: Locally
- Modulated by the Circle of Willis
- If the middle cerebral artery get blocked (thrombus), we can still get blood around the rest of the brain via some of the other collateral circulations
The Meninges: Seatbelts for the CNS - Sub-Dural Space
- Potential space
- Only a space when something gets in there
The Meninges: Seatbelts for the CNS - Sub-Arachnoid Space
- Actual space
- Where all the blood vessels are located
The Meninges: Seatbelts for the CNS - Dural Folds
- Falx cerebri: runs anterior and helps separate the two hemispheres
- Tentorium: separates the cerebrum from the cerebellum
- Locks the brain in place so it’s not moving around and bouncing off of the skull
- Support and restraint
Cerebrospinal Fluid
- Airbags of the CNS
- CSF in brain is constantly being made, circulates around and then is drained out with the deoxygenated blood
Blood-Brain Barrier: How is it Formed?
- Astrocytes: they wrap around the capillary and modulate what is allowed to come in and out
- Keeping the environment (CSF) stable
Blood-Brain Barrier: Crossing
- Small lipophilic molecules
- Molecules which have specific transporters e.g. glucose, amino acids
Blood-Brain Barrier: Things that Can’t Cross
- Various types of charged particles, other large molecules, immune cells
Blood-Brain Barrier: Things that Open the BBB
- Microwaves
- Radiation
- Trauma
- Hypertension
- Infection
Problems Created by the Protective Coverings of the Brain
- The cranium can’t expand
- If anything adds to the volume of the cranial contents - increase in intercranial pressure
- Things that would add to the volume:
> Oedema
> Abscess
> Tumour
> Space-occupying lesions
What Happens when a Space-Occupying Lesion Develops?
- CSF forced out of the cranium
- Less blood flows into the brain as the increased pressure inhibits in-flow
- Structures in the brain are compressed - herniations of tissue
Classic (Late) Signs of Raised ICP
- Deep, irregular respiration
- Widening pulse pressure
- Bradycardia
- Known as “Cushing’s Triad”
The Brainstem: Pons
- Has a lot of connections with the cerebellum
- Acts as a relay centre
- Gets a lot of information from the cortex and will send it to the cerebellum
The Brainstem: Functions
- Level of alertness
- Basic survival functions:
> Respiration
> Maintenance of BP - Controls breathing and heart beat
The Cerebellum
- Coordination and control of voluntary movements
- Postural adjustment during movements
- Advance planning of rapid movements
- Learning of movement sequences
- Helps provide smooth, coordinated body movement
The Limbic System
- Number of structures clustered around the brainstem
- Motivation (emotions) for survival purposes
- Learning and memory
- Linking of autonomic and endocrine responses to emotional states
- 4 Fs of survival: fighting, fleeing, feeding and fornicating
The Amygdala: Hub of Fear and Aggression
- Emotional learning: association of a sensory experience with an emotion (usually fear)
- Allows recognition of fear in others (facial expressions)
- Is strongly activated during exposure to aversive stimuli (visual, taste, auditory, smell)
People with Damage to Both Amygdala
- Do not show fear to stimuli that normally provoke a fear response
- Are unable to make risk assessments: benefit estimates and tend not to avoid an activity when the risk outweighs the benefit
- Are unable to recognise fearful expressions on faces
- Avoid eye contact during social interactions and stand closer to others during contact
