Chapter 2- Brain cells and nervous system organization Flashcards
Are reactions to the environment always planned?
Sometimes reactions to the environment are planned, some aren’t. Actions like squinting in bright light is unplanned, while drinking water is planned
2 general cell types of the nervous system
- Neurons- transmit information
2. Glia- act as supporting cells
Circuit
Neurons are organized in a precise order to form a circuit. A circuit is how information flows from one place to another. The two neurons could be close together or far apart (like with spinal reflexes).
Synapse
The synapse is the physical connection between 2 neurons where information crosses. This is how neurons communicate, and a single neuron could synapse with many other neurons at once.
All behavior arises from
Neurons- even if they’re few in number
Sensory neurons
Receive input
Motor neurons
Let the body move in a coordinated manner
Interneurons
Neurons that process information between sensory and motor neurons
Roundworm nervous system
302 neurons total, and they have a ganglion rather than a brain. Have very simple behaviors- move toward “good” things and away from bad things- based on light, pressure, moisture, etc.. Their sensory neurons detect light, smell, the presence of water, pressure. Because they have so few neurons, all of their neurons have been mapped. They are arranged in simple circuits that can produce simple behavior
Gill withdrawal reflex in sea slugs
A sea slug’s gill is retracted if you poke it- this is a protective reflex. However, if the tail is poked for a specific amount of times, it will stop retracting. The animals learned this after about 5 pokes,
For all mammals, the nervous system is divided into
The central nervous system (brain and spinal cord) and peripheral nervous system
Divisions of the peripheral nervous system (3)
- Sympathetic nervous system- fight or flight
- Parasympathetic nervous system- rest and digest, normal breathing and blood pressure
- Enteric nervous system- controls the gastrointestinal tract
How does having more neurons affect circuits?
More neurons- more complex circuits- more complex functions
The human nervous system
Has about 80 billion neurons, but also makes connections with hundreds of thousands of other neurons. Still uses sensory neurons to send info to the brain, interneurons process and make decisions, then send information to motor neurons. Humans have more neurons, more discrete brain regions, more complex circuits- capable of abilities that no other species on earth has.
Neurons
Neurons are the building blocks of the nervous system and the element of processing information. They are connected to each other via synapses to form circuits in all species
What aspects of the nervous system are shared between species?
Certain aspects of the nervous system are shared across all species (sensory neurons) and especially closely related species (brain and spinal cord in mammals).
Do circuits formed by neurons drive behavior in all animal species?
Yes, true for all animals
Camillo Golgi
Came up with staining technique to visualize the entire neuron. Thought neurons were continuous like tubing (not true)- he noticed that the processes of one neuron were very close to the other, and they looked like they touch under a microscope
Santiago Ramon y Cajal
Used Golgi’s method. Thought that neurons came close to each other, but did not touch (true)- there’s a small gap in between processes (this is the synapse). Also came up with the neuron doctrine
Neuron doctrine (2)
States that each neuron is an independent unit (a single processing unit) and information must be transmitted across gaps between neurons (synapses).
Neurons are polarized- what does this mean?
Polarized means that there is a direction to neurons- they aren’t symmetrical. There’s an input zone, then integration zone, conduction zone, and output zone.
Dendrites and spines
Dendrites look like branches, while spines look like mushroom shaped protrusions from the dendrites. These structures are the input zone- where information/chemical signals are received from other neurons
Soma
The cell body- this is the integration zone. The soma processes the electric information and decides what its response will be (or if it will even respond). Also contains organelles like the mitochondria, cell nucleus, and ribosomes.
Mitochondria function
Produce energy
Cell nucleus function
Contains genetic instructions
Ribosomes function
Translate genetic instructions into proteins
Axon hillock/axon initial segment
Final location where integration occurs and the decision to generate an electrical communication signal is made- most neurons have one axon hillock
Axon
- Conduct electrical signal on the cell membrane
- Transport material between the soma and the axon terminal- transports proteins in both directions
Axons can be very long- cell bodies in the spine send axons down to the toes
Types of axon transport (2)
- Anterograde= to axon terminal
2. Retrograde= from axon terminal (to cell body)
Axon terminal
Output zone- axon terminals from one neuron releases chemical signals onto many other neurons
In the nervous system, when is the signal electrical and when is it chemical?
In the neuron, the signal is electrical. Chemical when going across the gap (synapse)
Parts of the synapse (3)
Axon terminal, gap in between, then the dendritic spines. The chemical signal is released in the gap (synaptic cleft). Info transmission requires a lot of energy- mitochondria are required
Types of glial cells (3)
- Astrocytes
- Oligodendrocytes/Schwann cells
- Microglial cells
Astrocytes functions (4)
- Monitor and support the metabolic and biochemical needs of neurons
- Regulate synaptic signaling as part of the “tripartite synapse”.
- Help form the blood brain barrier by sitting between blood capillaries and neurons
- React to brain injury (repair and scarring)
Tripartite synapse
3 parts- presynaptic axon terminal, postsynaptic dendritic spine, and the astrocyte. Refers to the functional integration and proximity of the astrocyte to the neurons in the synapse.
Blood brain barrier
The blood brain barrier isolates the brain from the rest of the body to protect it (an infection that spreads to your brain would be really bad). Blood vessels are on the outside of the barrier, so whatever is in the blood doesn’t necessarily get into our brain. This is literally a barrier (membrane) that things have to cross to get to the brain, formed by astrocytes.
Oligodendrocytes location
CNS
Schwann cells location
PNS
Myelin
A lipid substance that insulates the axon to speed up the electrical signal- secreted by the glial cells.
Oligodendrocytes and Schwann cells function
Insulate axons by wrapping myelin around them- white matter
Nodes of Ranvier
Gaps in the myelin sheath, very important with how information is sent down the axon
Microglia functions (2)
- Monitor local environment for threat or injury
2. Migrate to injury site to remove debris/dead cells
Why are microglia necessary?
The microglia are brain immune cells similar to macrophages. The blood brain barrier prevents the immune system from entering the brain- the brain has its own immune system. With an injury, local neurons release signals. The microglia will be attracted to the site and attract other microglia.
Gross anatomy
Neural structures that you can see with your eyes.
Horizontal plane
Splits the body into upper and lower halves
Sagittal plane
Splits the body into right and left sides
Dorsal
Towards the top of the brain. When humans became upright, the brain curved, so that’s why dorsal is the top.
Ventral
Towards the bottom of the brain
Caudal
Posterior, toward the back of the brain
Rostral
Anterior, toward the front of the brain
Coronal plane
Splits the body into front and back halves
The central nervous system is composed of
The brain and spinal cord
The peripheral nervous system is composed of
All parts of the nervous system outside of the brain and spinal cord
Nerves
Bundles of axons in the PNS
Ganglia
Clusters of neuron cell bodies distributed throughout the body (near spine or near organs)
The PNS is divided into (2)
- Somatic nervous system
2. Autonomic nervous system
The somatic nervous system is composed of
Nerves between brain/spinal cord and skeletal muscles/sensory organs
The autonomic nervous system is composed of
Nerves between brain/spinal cord and internal organs
Nerves from the somatic nervous system control which functions?
Voluntary movements- something you choose to do, like walking
Which sections of the spinal cord are responsible for sensory vs motor information?
Sensory information travels along the dorsal root, motor information travels along the ventral root.
How does the somatic nervous system function?
Nerves send information from sense organs to the brain/spinal cord, nerves from the brain/spinal cord travel to the skeletal muscles. Sensory information about the environment goes to the CNS, motor information is your response that goes from the CNS to the PNS- you need at least 2 neurons.
In the somatic nervous system, information goes from
Information always goes from dorsal to ventral- the dorsal nerve is the input of sensory information
Divisions of the autonomic nervous system (3)
- Sympathetic
- Parasympathetic
- Enteric
In general, what functions does the autonomic nervous system control?
Involuntary movements/actions
Sympathetic nervous system
Uses norepinephrine as a neurotransmitter. Carries out the fight or flight response- activates the body to confront a challenge. The body is oxygenated, slows down digestion
Parasympathetic nervous system
Uses acetylcholine as a neurotransmitter. Known for rest and digest- normal heart rate and digestion.
Enteric nervous system
Responsible for gut/digestive control. A lot of bacteria live in the gut, and can send signals to the brain to influence mood and behavior.
What general functions is the CNS responsible for? (5)
- Senses- vision, sight, and others
- Initiating movement of your muscles vs moving
- Higher order behavior- attention, cognition, perception, thought, affect, mood
- Automatic life essential functions- breathing, hunger, thermoregulation, circadian rhythm. Directs the ANS.
- Integrating and sending out information
What general functions is the PNS responsible for?
Actual sensing of information occurs in the PNS, and it sends the information to the CNS to be interpreted.
Sections of the spinal cord (5)
Cervical (neck), thoracic (trunk), lumbar (lower back), sacral (pelvic), coccygeal (tail bones)
How many pairs of spinal nerves?
- One nerve serves the left side of the body, the other the right. The nerves on the left side receive information from the left side of the body and vice versa
How does the dorsal root ganglion participate in spinal reflexes?
Sensory information comes in through the bipolar neuron, which has a very sensitive axon hillock. Information goes straight to an axon (no cell body), which goes right to the axon terminal. It then goes to an interneuron in the spinal cord, which sends motor information straight from there. This is because information must be transferred very quickly to the spinal cord
How does the ventral root participate in spinal reflexes?
Cell bodies are located in the ventral horn. it send the axon to the effector muscle to make it move as a motor response.
Sulcus
a groove in the cerebral cortex (sulci is plural)
Gyrus
matter between two grooves/wrinkles (gyri is plural)
What is the purpose of gyri and sulci?
These increase surface area- fits more brain tissue into a smaller space, since it’s folded
How is the brain organized?
Brain regions don’t generally function in isolation- some regions might be central locations for one behavior, but other regions are likely involved. In addition, most brain regions have many functions.
4 lobes of the cerebral cortex
- Frontal lobe (at the front)
- Parietal lobe (top of the head)
- Temporal lobes (sides- there are 2 of them)
- Occipital lobe (at the back)
Central sulcus
separates the frontal and parietal lobe
Sylvian fissure
separates the frontal and occipital lobe
Longitudinal fissure
separates the left and right hemispheres
White matter
Light brain tissue- axons with myelin sheaths on the inside of the brain
Gray matter
Dark brain tissue- cell bodies and dendrites on the outside of the brain
Which cerebral cortex lobes can be seen from the ventral view of the brain?
Frontal and temporal lobes
Tracts
Bundles of axons in the brain. Brain regions use tracts to communicate.
Nerves
Bundles of axons in the PNS
Corpus callosum
Axon tract that joins the two hemispheres, lets information flow between the sides of the brain. Sometimes, the corpus callosum is cut surgically to control severe seizures. It can affect the ability to integrate information in adults, but children can form more connections. Only done if a person is having very severe seizures, like 8-10 per day
What general function is the cerebral cortex responsible for?
Complex thought and function
Frontal lobe functions
movement, high level cognition
Parietal lobe functions
Body’s sensory information, touch- where the fingers are in space, determining how something feels
Temporal lobes functions
hearing, smell
Occipital lobe function
Vision
Parts of the sensory cortex (3)
- Primary somatosensory cortex
- Visual cortex
- Auditory cortex
Primary somatosensory cortex
Located in the parietal lobe. First area of processing- sends information to the motor cortex so it can send out a response
Visual cortex
Located in the occipital lobe. First area of processing.
Auditory cortex
Located in the temporal lobe. First area of processing
Motor cortex
Responsible for generating motor responses, contains the primary motor cortex
Associative cortex
Responsible for the integration of sensory inputs and helps plan motor functions. Contains the prefrontal cortex, which is responsible for planning, decision making, etc.. Young adults/teenagers tend to make risky decisions since the prefrontal cortex isn’t completely developed.
Homunculus
The primary motor cortex is anterior to the central sulcus, while the primary sensory cortex is posterior to the central sulcus. There is a direct one to one connection between the brain and the other body areas on the diagram (both sensory and motor).
The 6 layers of the cerebral cortex
Cell bodies form different layers of the cortex. Layers 3 and 5 contain pyramidal neurons, which are projection cells that send their myelinated axons across the brain. Their apical (top) and basal (bottom) dendrites receive information. The basal dendrites surround the cell body and receive different types of information
Thalamus
Thalamus- sensory relay region- sends sensory information to the right place
Hypothalamus
Neurohormone center, along with the pituitary gland
Limbic system function
Emotion and learning
Parts of the limbic system (2)
- Amygdala
2. Hippocampus
Amygdala
Center for negative emotion, fear, anxiety. Negative emotion (like injury from touching something hot) improves learning, as do positive emotions. You don’t tend to remember normal everyday events without strong emotions
Hippocampus
Learning and memory formation
Basal ganglia
Center for motor control. Contains the substantia nigra, where neurons contain the neurotransmitter dopamine. This is where neurons start to die if you have Parkinson’s disease.
Nuclei
Brain region
Pons
Motor control and sensory nuclei, some cranial nerves originate here
Medulla
This is where the brain connects to the spinal cord. Controls breathing and heart rate. Some of the cranial nerves that control functions in the face and neck originate here.
Regions of the brain stem (2)
- Pons
2. Medulla
Cerebellum functions (3)
- Fine motor control
- Gait, balance- alcohol affects this region to cause difficulty balancing while walking
- Muscle coordination
