The Human Brain Flashcards
3 main components of the CNS
- Neuron
- Glia cells
- Vasculature
Neuron
• A neuron is the basic signaling unit of the nervous system and which supports cognition
• Each neuron receives and combines multiple inputs to determine whether to transmit an action potential to the next target in the network
○ Axons (connecting fiber) send signals (axon terminals: at end of neuron)
○ Dendrites receive signals
○ Schwann cells: make myelin
- Myelin sheath : insulating fatty layer that speeds transmission
Glia cells
Provide support functions both chemically and structurally
• There are equal numbers of glia and neurons but different glia/neuron ratios in different structures in the human brain
○ Cerebellum: 0.23
○ Grey matter of cerebral cortex: 1.48
○ Rest of brain 11.35
• Main types of glia
○ Astrocytes: form the blood-brain barrier
○ Oligodendrocytes & Schwann cells - myelin production
○ Microglia : remove foreign & damaged cells
Vasculature
the arrangement of blood vessels which take blood to and away from the brain
Classification of neurons by shape
○ Unipolar: common in inverterbrate NS
○ Bipolar: found in some sensory systems incl the retina & olfactory system
○ Pseudounipolar: convey information from receptors in joints, muscles, and skin in the central nervous system
Multipolar: most neurons
Functional classification of neurons
○ Afferent (sensory) neurons: convey information from tissues and organs into the central nervous system
○ Efferent (motor) neurons transmit signals from the central nervous system to the effector cells.
Interneurons(association neurons) connect neurons within specific regions of the central nervous system.
Neurotransmitters
chemicals such as acethylcholine, serotinin, histamine, dopamine or oxytocin responsible for sending nerve signals across a synapse between 2 neurons (into the synaptic cleft)
How are neurotransmitters removed after they are released
○ Are removed after released by either 3 processes:
1. Active reuptake back into the presynaptic terminal
2. By the enzymatic breakdown of the chemical in the synaptic cleft
3. By diffusion, and away from the region of the synapse
Action potential
A sudden change (depolarization & repolarization) in the electrical properties of the neuron membrane in an axon
○ Consists of a no of phases
Graded potential
○ Some neurons do not generate action potentials, but instead generate a graded electrical signal, which in turn causes graded neurotransmitter release.
Such non-spiking neurons tend to be sensory neurons or interneurons, because they cannot carry signals long distances
Response rate
• Neurons code information in terms of a response rate, which is also called the spiking rate
○ Information is carried in the response rate of neurons
○ Different neurons respond in different situations, which shows the functional specialization of brain regions
- Neurons responding to similar types of information tend to be grouped together
○ The input and output of a neuron determines the type of information that neuron encodes
Synaptogenesis
The formation of synapses between neurons (creation of new synapses)
○ New synapses are also formed during learning and synaptic repair
Pruning
Refers to the elimination of synapses to increase the efficiency of neuronal transmissions
○ Grey matter volume declines from age 4-20
Neurogenesis
Refers to the formation of new neurons, this occurs throughout life
Gross organization of the brain
• Neurons group together to form
○ Grey matter: areas rich in neuronal cell bodies which are arranged in layers to form a sheet of tissue
○ White matter: bundle of axons and glial cells forming tracts interconnecting the brain
• The brain consists of highly convoluted sheets of grey matter (cortex) on top of white matter, underneath which lies another collection of grey matter:
○ Basal ganglia
○ Limbic system (hippocampus, amygdala & septum)
○ Diencephalon: thalamus & hypothalamus
• The cortex is composed of several layers (6) : thickness ranges from 1.5mm to 4.5mm
Most recent models of the brain show 210 cortical and 36 subcortical subregions
Sulci and fissures
• The sulci and fissures are both grooves in the cortex but they are differentiated by size
○ A sulcus is a shallower groove that surrounds a gyrus
- A fissure is a large furrow that divides the brain into lobes and also into the 2 hemispheres ( the longitudinal fissure)
The Forebrain
Made up of the:
• The Cerebral cortex: the outer layer of the cerebral hemispheres
○ Its functions include the processing of information, thinking and planning
• The basal ganglia are crucial to the function of the motor system
• The limbic system is involved in learning, emotions and motivation
- It includes the hippocampus, amygdala & septum
• The thalamus: is the primary relay station for sensory information coming into the brain
- The hypothalamus controls the endocrine system and the autonomic nervous system (body temperature, appetite and thirst regulation)
The Midbrain
• The reticular activating system (RAS) is important in controlling consciousness: (sleep, arousal), attention, cardiorespiratory function and movement
○ It extends into the hindbrain
- Other structures involved in vision, hearing and controlling movement
The Hindbrain
- The cerebellum is essential to balance & coordination of muscles (dexterity and smooth coordination of movement)
- The pons is involved in consciousness
- The medulla oblongata regulates vital functions and is involved in cardiorespiratory function, digestion and swallowing
The cerebral cortex (cerebrum)
• The cerebral cortex (cerebrum) is the largest part of the brain associated with higher brain function such as thought and action. It is further divided into 4 sections called lobes:
○ Frontal lobe
○ Parietal lobe
○ Occipital lobe
- Temporal lobe
The frontal lobe
- Memory
- Decision Making
- Reasoning
- Emotion regulation
- Personality
- Motor control
- Language
The Parietal lobe
- Senses and integrates sensation
- Spatial awareness and perception
- Proprioception (awareness of where parts of our bodies are)
The Occipital lobe
- Processing, integration and interpretation of VISION
The Temporal lobe
- Hearing
- Organization & Comprehension of language
- Memory & Memory formation
