The Brain Flashcards
What is the central nervous system
The spine and skull
What is the peripheral nervous system
Everything outside the spine and skull
Contains nerves and ganglion
Can regrow after damage
Afferent information (PNS)
Input from the sensory division
Efferent information (PNS)
Output from the motor division
What are neurones
Nerve cells that are electrically excitable communicate with other cells via specialises connections called synapses.
They make up the majority of nervous tissue
What are glial cells
Non-neuronal cells in the nervous system that maintain homeostasis, form myelin, and provide support and protection for neurones
What does the dendritic pattern indicate
The number of inputs (and the information) received by a neurone
Information passed within neurones is…
Electrical
Information passed between neurones is…
Chemical
Role of oligodendrocytes
- Form the myelin sheath on axons in the CNS
- Each oligodendrocyte can myelinated up to 50 axons
Role of Schwann cells
- Form myelin in PNS
- Assist in regeneration and re-growth of axons
Role of microglia
- The brains immune system
- Scavenge the CNS for plaques, damaged cells and infectious agents
Role of ependymal cells
- Make up a membrane called the ependyma which is a thin membrane lining the central canal of the spinal cord and the ventricles
- Produce cerebrospinal fluid
Role of atrocytes
- Regulate chemicals around neurones (glucose, ion concentration, neurotransmitter uptake)
- Regulate blood flow around the brain (vasomodulation)
- Nervous system repair (fill spaces in the NS creating glial scars)
- Maintenance of the blood-brain barrier
What are the 5 types of glial cells
- Oligodendrocytes
- Schwann cells
- Astrocytes
- Microglia
- Ependymal cells
What is the role of myelin
Allows axon potentials to propagate quicker
Unmyelinated speeds = 0.5-10m/s
Myelinated = 150m/s
Brain stem
Sits at the top of the spinal cord and is made up of 3 parts;
- medulla
- pons
- cerebellum
What is the role of the medulla
Controls basic motor functions (cardiac, respiration and reflexes)
What is the role of the pons
Contains nuclei that relay signals from the forebrain to the cerebellum
The nuclei deal primarily with sleep, respiration, swallowing, bladder control, hearing, posture etc.
What is the role of the cerebellum
Maintenance of balance and posture
Coordination of movements
Motor learning
Role of midbrain
- Tectum controls rapid orientation of head and neck
- Also associated with sleep wake cycles, alertness and temp regulation
Role of thalamus
Takes information from the periphery and passes it onto the cortex
Role of basal ganglia
- Movement regulation
- Skill learning
- Habit formation
- Reward systems
- Selection of appropriate behaviours
- Self-inhibition of behaviours
Role of the cerebral cortex
- Movement
- Attention
- Perception
- Awareness
- Thought
- Memory
- Language
- Conciousness
What is the cortical sheet
Has 6 layers that are highly folded with folds (gyri) and grooves (sulci)
How do you count brain cells
Brain cells can be measured by dissolving the cells and surrounding structure but leaving each cell nuclei whole
These nuclei are an isotropic suspension
How much energy does the human brain consume
20% of the total energy generated in the body
What percentage of body weight is the brain
2%
How much cardiac output is directed to the brain
15-20%
What is the marker for the tissue uptake of glucose
Flurodeoxyglucose (18F-FDG)
What is the middle of the spinal cord made of
Neurones and other cells (grey matter)
What is the outside of the spinal cord made of
Fibres (white matter) that carry information up and down the cord
Where does sensory information come from
Sensory information comes into the spinal cord at the dorsal horn
Where are motor neurones located
In the ventral spinal cord
What are the 2 major descending systems
Lateral descending system
Medial descending system
What is the lateral descending system
The corticospinal and rubrospinal tracts
Where are the fibres of the lateral system located
In the dorso-lateral part of the spinal cord
They connect to motor neurones in the lateral part of the ventral horn
What is the medial descending system
The vestibulospinal and reticospinal tracts
Where are the fibres of the medial system located
In the ventro-medial part of white matter
They connect to motor neurones in the medial part of the ventral horn
Role of the dorsal column pathway
Carries sensory information from the joint and skin
Role of the spinothalamic pathway
The lateral spinothomatic tract conveys crude touch, pain and temperature
What are the dorsal root ganglion
The cell bodies of incoming sensory neurones lie outside the spine in a series of ganglion
How many pairs of spinal nerves are there
31
What are dermatomes
An area of the skin supplied by nerves from a single spinal root
What is rate coding in the motor system
Motor neurones use a rate code to signal the amount of force to be exerted by a muscle
What is the vestibulospinal system
The sensory system that provides the sense of balance and spatial orientation for the purpose of coordinating movement with balance
What is the vestibulospinal tract
Originates in the vestibular nuclei
They send most of their output to the spinal cord and to the muscles that move the eyes
What is the reticular formation
A set of interconnected nuclei located at the bottom of the brain stem
What is the reticulospinal tract
Originates in reticular formation
These tracts function in maintaining tone, balance and posture
What volume of the brain does the cerebellum take up
10%
What is the input : output connections ratio in the cerebellum
40:1
How many neurones are in the cerebellum
69B
Superior cerebellar penduncle
Efferent (out) pathway to the red nucleus and the cortex (via the thalamus) and sup colliculus
Middle cerebellar penduncle
Most fibres originate in the pons
Input from sensory, visual, vestibular and motor systems
Largest input is from the cortex
Inferior cerebellar peduncle
Carries information to and from the spinal cord (and the body) and vestibular nuclei
What is the red nucleus
A roughly spherical collection of cell bodies in the midbrain
It is extremely vascular
It receives a very large input from the cerebellum and from the primary motor cortex
Role of basal ganglia
- movement regulation
- skill learning
- habit formation
- reward systems
- selection of appropriate behaviours
- self-initiation of behaviours
Direct pathway through the basal ganglia
Short loop
Has excitatory effect on cortex
Net effect is pro-movement
Indirect pathway through basal ganglia
Long loop
Has inhibitory effect
Net effect is anti-movement
Primary motor cortex
Neurones in the primary motor cortex have a simple relationship to movement
They fire around 5-100ms before movement onset and can code for the basic parameters of movement ie, force, direction, extent, speed
Non-primary motor cortex
Neurones in the non-primary motor cortex have a more complex relationship to movement
They code more complex aspects like pre-motor cortex and supplementary motor cortex
Pre-motor cortex
- planning movement
- spatial guidance of movement
- sensory guidance of movement
Supplementary motor cortex
- coordinating temporal sequences of actions
- bimanual coordination
- initiation of internally generated as opposed to stimulus driven movement
Primary sensory cortex
Touch - vibration, pain, heat, pressure
Proprioception - afferent information eg, joint position sense, kinaesthesia, sensation of resistance
Posterior parietal cortex
Integration of sensory and visual information to execute complex movement in the environment
What is the corticospinal tract
The most important tract in the human for precise control of the limbs
Origin of the corticospinal tract
Primary motor cortex (30%)
Premotor, supplementary (30%)
Somatosensory, parietal, cingulate (40%)
How many fibres are in the corticospinal tract
1 million
90% cross at lower medulla
