10/13: Higher Brain Functions

The Nervous System

• Made of CNS and PNS 

Central Nervous System (CNS)

• Brain and spinal cord

Peripheral Nervous System (PNS):

• Everything else that is not the brain and spinal cord

• Cranial and spinal nerves

Reflex arc

• A neutral pathway that produces a fast response to a stimulus

How does the signal pass through the reflex arc?

1. Receptor 

2. Sensory Neuron

3. Association Neuron 

4. Motor Neuron

5.  Effector 

Receptor 

• Can be pain receptors

• Stimulated by change in environment

Sensory Neuron

• Also called afferent neuron

• Receptor send signal to the afferent neuron 

• Part of the Peripheral Nervous System

• Outside the central nervous system. Will enter the spinal cord

Association Neuron 

• Also called interneuron 

• Sometimes skipped

• Inside the spinal cord (Central Nervous System)

Motor Neuron

• Also called efferent neuron

• Leaving the spinal cord

• It will interact with the effector

Effector 

• The muscle or gland that is going to respond to that signal

Where is sensory information in the reflex arc?

• Sensory (afferent) impulses travel through the dorsal (back) spinal cord

 Where is motor information in the reflex arc?

Motor (efferent) impulses travel through ventral (front/belly) spinal cord

Neurons in the Posterior Column Pathway

• Neuron #1: 1st order neurons

•  Neuron #2: 2nd order neuron

• Neuron #3: 3rd order neuron

 Neuron #1: 1st order neurons

• From: receptor in skin/muscle/joint

• To: Brain

• Function: detects stimulus in the peripheral system and sends it to the CNS

• This neuron is super long

Neuron #2: 2nd order neuron

• From: Brain stem

• To: thalamus

• Function: Relays signal and often undergoes decisions (crosses to the opposite side of CNS)

Medulla oblongata

• Regulate involuntary in automatic function like breathing, heart rate

Thalamus

• The information center for all sensory information

Pathway is decussation

Crossing over to the opposite side of that central nervous system

Neuron #3: 3rd order neuron

• From: thalamus

• To: Primary somatosensory cortex (brain)

• Function: Allow conscious perception of the sensation 

Homunculus

• Map like representation of the human body that shows how different body parts correspond to areas of the cerebral cortex 

Sensory homunculus

• Maps body parts to the somatosensory cortex for sensation

Primary Somatic Sensory Cortex

• Located in the postcentral gyrus of the parietal lobe. Receives and process sensory information such as touch, pressure, pain, temperature, and body position.

Post central gyrus

• Location in the brain where we are experiencing senses

Have a lot of neurons on

hands, tongue, lips

Motor signals don't happen in a sequence.

• It is going all over the place

Primary Motor Cortex (M1)

• Initiates movement

• Located in the precentral gyrus of the frontal lobe. Controls voluntary muscle movements.

• Send signals to activate specific muscle like, arms, hands and fingers to grasp the cup

Supplementary Motor Cortex (SMA)

• Learned sequence of movements

• Ex: Drinking from the cup multiple times

Posterior Parietal Cortex (PPC)

• Movements are targeted accurately toward objects in place

• Ex: If I want to pick up my cup, this part of the brain will figure out where my body and the cup are in space. Create a spatial plan to allow me to get to the cup.

Premotor Cortex (PMA)

• Organizes motor functions before initiation

• Ex: Plan out how my arm is going to move toward the cup. Choose the muscle and the movement patterns based on my visual cue to get to the target

Motor homunculus

• Maps body parts to the motor cortex for movement.

Corticospinal pathway

• It takes 2 neurons to bring signals from the brain to the skeletal muscles in the corticospinal pathway.

• Upper motor neuron and Lower motor neuron

Upper motor neuron

• From cortex to spinal cord

Lower motor neuron

• From spinal cord to skeletal muscles

Descending motor pathways include

• brain areas that produce dopamine 

Substantia nigra

• Dopamine producing cells

• When there is a damage to the substantia nigra, the production of dopamine decrease

• Will lose 5 to 10% of dopamine every decade of aging

• Will affect people and they will have parkinson’s disease

Dopamine

• A neurotransmitter responsible for muscle movement

Parkinson’s disease

• Related to the decrease in dopamine 

 What are some non-motor symptoms of Parkinson’s disease?

• Loss of sense of smell

• Drooling

• Constipation and gastrointestinal problem

• Sleep problems such as restless leg syndrome

• Mark like facial expression

 What are some motor-related symptoms of Parkinson’s disease?

• Stowed movements

• Tremor while muscles are at rest

• Rigidity or stiffness

• Blinking less often than usual

• Trouble swallowing

• Unstable posture or walking gait

How does exercise reduce symptoms and the progression of Parkinson’s disease

• It leads to regeneration of damaged nerve tissues

• It improves metabolism and immune responses

• It stimulates neurogenesis (making new neurons) → Improve signal processing

• It strengthens synaptic strength

The central nervous system consists of the brain and spinal cord. Which type of neuron exists completely within the CNS? This type does not extend into peripheral nervous system or exit the CNS.

Interneuron/association neuron

How many neurons are involved in bringing sensory signals to the brain in the posterior column pathway?

• 3

What are the two subdivision for motor (efferent)

• Somatic and Autonomic

Somatic

• Voluntary

• Skeletal muscles

Autonomic

• Involuntary

• Cardiac and smooth muscle glands

What are the two divisions of the autonomic nervous system (ANS)?

• Sympathetic

• Parasympathetic

Sympathetic System

• Fight or Flight

• Prepares your body for stress, danger, or activity

• Heart rate increases, pupils dilate (get bigger), digestion slows down, airways widen, saliva decreases, bladder helps retain urine

Parasympathetic System

• Rest and digest

• Helps your body relax, digest food, and conserve energy

• Heart rate decreases, pupils constrict (get smaller), digestion increases, airway narrow toward resting state, saliva increases, bladder promotes urination