Lecture 1 A Tour of the brain Flashcards
Role of neurons
receive, carry and process information in the form of electrical and chemical signals. Carry out neuronal computations that underpin cognitive and mental operations
How many neurons in human nervous system
90 billion
Role of glial cells (Glia)
Provide support to the neurons
How may Glial cells in the nervous system?
As many glial cells as neurons
Basic structure of neurons: Dendritic tree
receive, carry and process information in the form of electrical and chemical signals
Basic structure of neurons: Cell body
- contains the cellular machinery that maintains the neuron’s health.
- Integrates information received from dendrites
Basic structure of neurons: Axons
- Sends information to other neurons or to other organs (e.g., muscles)
- Can divide into axon terminals
Main types of neurons: Sensory
Bring information to the central nervous system
Main types of neurons: Interneurons
Integrate/ associate sensory and motor information in the central nervous system
Main types of neurons: Motor neurons
Send information from the central nervous system to muscles
What happens at the synapse?
The meeting of an axon terminal of one neuron onto the dendrites of another neuron
Roles of glial cells in the nervous system
- Structure
- Provide energy and nutrients to neurons by connecting them to the vascular system
- Blood-brain barrier, preventing some substances from passing from the vascular system to the nervous system
- Aid re-organisation of the system following brain damage
- Increase transmission speed of electrical information between neurons
- Modulate neuronal transmission of information
Examples of glial cells: Astrocytes
- Intermediary between neurons and vascular system
- Provide energy to neurons
- Participate in the blood-brain barrier
Examples of glial cells: Microglia
Phagocyte dead cells
Examples of glial cells: Oligodendrocytes:
Provide insulation to axons, speeding up electrical transmission
Neural structures: Nerves
A bundle of axons
Neural structures: White matter
nervous tissue made mostly of axons and myelin
Neural structures: Nuclei and ganglions
group of neurons (mainly cell bodies)
Neural structures: Grey matter
Nervous tissue made mostly of neurons
Neural structures: Cortex
Grey matter organised into layers
Anatomical orientation terms: Lateral
Towards the outside (left or right)
Anatomical orientation terms: Medial
Towards the middle
Anatomical orientation terms: Contralateral
The opposite side
Anatomical orientation terms: Ipsilateral
the same side
Anatomical orientation terms: Unilateral
One side of the brain
Anatomical orientation terms: Bilateral
Both sides of the brain
Anatomical sections: Sagittal section
Divides the brain into left and right parts
Anatomical sections: Coronal section
separates front brain from the back
Anatomical sections: Horizontal or axial section
Splits brain into upper and lower sections
Major subdivisions of the nervous system: CNS
- Brain and spinal cord
- Encased in skull (brain) and spine (spinal cord) for protection
Major subdivisions of the nervous system: PNS
Any part of the nervous system outside skull and spine
Peripheral nervous system:
- Mostly nerves (axons) with some neuronal bodies in ganglion
- Most nerves enter/exit the spinal cord (except cranial nerves)
Somatic nervous system
Sensory nerves: Carry information about the outside world from sensory organs to CNS (afferent information) Conscious perception
Motor nerves: carry motor commands from CNS to muscles (efferent information) Voluntary movements
Autonomic nervous system
- Involuntary/unconscious
- Visceral functions e.g., digest, breathing
Branches of autonomic nervous system
Sympathetic branch: Prepares the body for action
Parasympathetic branch: Maintains bodily functions
Involved in expressing emotion
Cranial nerves key point
Connect to the CNS at the level of the brain (instead of the spinal cord)
The possible various functions of cranial nerves
- Receives sensory information
- Controls facial muscles
- Vagus nerve: send/receive information to the parasympathetic nervous system
Subdivisions of the CNS: The spinal cord
- Relays sensory and motor information to and from the brain
- Dorsal section: sensory functions
- Ventral section: motor functions
- White matter: sensory and motor nerve fibres (axons)
- Grey matter: neuronal bodies, interneurons (involved in arc reflex, e.g., knee reflex)
- Different parts of the spinal cord receive information from, and control, different parts of the body
Subdivisions of the CNS: The brain stem: medulla
- Directly superior to spinal cord
- Vital reflexes
- Reticular activating system: controls arousal and sleep-wake cycle
- Motor nerves from the brain contralateral side of the body
- Point of entry of cranial nerves 9-12:
- Damage could lead to death as controls vital functions
Subdivisions of the CNS: The brain stem: pons
- Mainly white matter tracts connecting the brain to cerebellum
- Point of entry for cranial nerves 5-8
Cerebellum
- ‘small brain’
- Organised in layers of neurons (cortex), with white matter in-between
- 5x more neurons than the cerebral cortex
- Connected to the brain stem at the pons
- Receives sensory and sends motor information
- Main functions: fine guidance of motor activity, balance, fluidity and precision of mental processes
- Damage will lead to problems with coordination, balance, posture and speech
The brain stem: midbrain
Contains
- Inferior colliculus: orientation to auditory stimuli
- Superior colliculus: orientation to visual stimuli
Head and eye movements towards sensory stimuli
Point of entry for cranial nerves 3-4
- Eye movements
The diencephalon: thalamus
Made of nuclei, each specialised in different sensory or motor functions
Sometimes called the “gateway” to the cortex relays information:from the peripheral sensory system to the cerebral cortex, from motor cortex to muscles
The diencephalon: hypothalamus
Maintains the body’s equilibrium
Connected to the hormonal system controls: sexual behaviour, circadian rhythms, fight/flight
Dysfunctions can lead to disturbed sleep, body temperature, growth, weight
Cerebral cortex and subcortical nuclei: basal ganglia
- lateral, anterior and central to the thalamus
- Role in motor control
- Damage = involuntary movements, tremors
Cerebral cortex and subcortical nuclei: Amygdala
Sometimes included in the basal ganglia
Role in emotions (part of the limbic system, together with the hypothalamus, the hippocampus and other structures)
Cerebral cortex
Folded sheet of grey matter (1.5 to 4.5 mm thick, ~0.25 m2).- Outward fold/bump = gyrus,
- Inward fold/groove = sulcus,
- large sulcus = fissure
Six cortical layers in most parts of the cortex
Two cerebral hemispheres, functional differences
Four main lobes + insula
Underpins most higher-level cognitive functions (object recognition, attention, memory, action planning,)
Cerebral cortex: anatomical subdivisions:
Each gyrus and sulcus has it’s name
Exact shape and location varies between people
Cerebral cortex: cyto-architectonic subdivisions: Cytoarchitectonic/laminar organisation:
Relative thickness of different neuronal layers
Cerebral cortex: cyto-architectonic subdivisions: Brodmann areas
Different cortical areas have different laminar organisations.
Cortex can be subdivided into cortical areas with similar laminar organisation.
Hypothesise that different brodmann areas may have different functions.
Cerebral cortex: functional subdivisions
Lesions in different regions of the cortex result in different deficits
Neuroimaging studies: different tasks activate different cortical regions
However, one behaviour probably engages many regions, one cortical region may be engaged in different behaviours
Protection of CNS
Skull/spinal column
Meninges: layers of tissue between bone and brain/spinal cord
Protection of CNS: Cerebrospinal fluid (CSF):
- Similar composition to blood but no red blood cells
Fills, meninges, central and central canal of spinal cord
Brain floats in CSF, which acts as a cushion
